bluuebunny/crossref_metadata_2025 huggingface dataset:
Organic carbon isotope ratios and paleoenvironmental implications for Holocene sediments in Lake Melville, southeastern Labrador
Authors: Tan F. C. , Vilks G.
Published: June 2009

Stable isotope 13C/12C ratios of organic carbon in sediments and in particulate organic carbon (POC) change from typically marine values in Groswater Bay to those of terrestrial soils in Goose Bay along an offshore–onshore transect in Hamilton Inlet, southeastern Labrator. The δ13C values in POC collected from close to the water surface change relatively little in Lake Melville, indicating that the integrity of the runoff plume is maintained as it spreads in Lake Melville. The organic carbon isotope ratios in POC collected from the near-bottom waters are similar to those of surficial sediments.Downcore δ13C values reflect paleo-oceanographic changes in Hamilton Inlet during and since deglaciation. In two sediment cores that reached sufficiently old sediments (10 000 years BP), the δ13C values change toward the bottom of the cores to values similar to those of the terrestrial organic carbon in soils, signifying greater terrestrial influence during deglaciation and during the early Holocene.According to the history of postglacial isostatic readjustment of the area, Lake Melville basin was more open to the marine waters during the early postglacial marine incursion because of deeper channels leading into Lake Melville. As a consequence, evidence for greater marine influence during that time should be found in sediment cores. The lack of evidence for the deposition of marine organic carbon brought in by the marine counterflow waters suggests a proximal glaciomarine environment in the Lake Melville basin. Glacial runoff diluted the basin waters, and it is possible that the whole inner Labrador Shelf was relatively fresh during that time.
Genesis of carbonate till in the lee sides of Precambrian Shield uplands, Hemlo area, Ontario
Authors: Hicock Stephen R.
Published: June 2009

Near Hemlo, Ontario, highly calcareous till is confined to areas located downglacier from Precambrian uplands, at least 150 km from the Paleozoic–Precambrian boundary. It comprises subglacial meltout till between lodgment tills, and the calcareous package overlies noncalcareous basal till (not studied) and underlies noncalcareous supraglacial meltout till. The tills can be distinguished by textural, carbonate, and clast compositions. Glaciotectonic deformations, stone fabrics and striae, and stone provenance from the tills, as well as erosional and depositional landforms, indicate that ice advanced to the south–southwest across bedrock contacts and over Precambrian uplands.Deposition of all five tills can be explained with one glacial event. As the Late Wisconsinan margin of the Laurentide ice sheet advanced against uplands about 20 km northeast of Hemlo it experienced compressive flow while depositing the non calcareous basal till. Upshearing of stoss-side local debris high into the ice also occurred as englacial ice overrode the slowed basal zone. Once over the upland, englacial ice assumed extending flow, and downshearing of distal debris, which was deposited as calcareous lodgment till on the lee sides of uplands. After the glacial maximum, the glacier ceased internal movement and subglacial meltout till was laid down. A late reactivation of the ice deposited the upper lodgment till and final stagnation formed the supraglacial meltout till.
Magnetic and pebble fabrics and origin of the Sunnybrook Till, Scarborough, Ontario, Canada
Authors: Gravenor C. P. , Wong T.
Published: June 2009

The early Wisconsinan Sunnybrook Till is a mud-rich, pebble-poor, dark gray to gray–brown massive diamicton that is exposed in the Scarborough Bluffs, Ontario. It is interpreted here to be till.Previous separate, magnetic, and pebble fabric studies made on the till suggest a westward ice movement ranging from west of south to northwest. In this study, two dominant directions are found, northwest by west and northeast by north. Of these two directions, the northwest by west direction is the most common and this combined with the direction of shear in the underlying sediments and lithology of the till suggests that the glacier moved in a westerly direction.However, the fabrics are not typical of a lodgement till and to some extent resemble fabrics found in subaquatic debris-flow deposits. It is suggested that the glacier that deposited the Sunnybrook Till was buoyed up by high pore water pressure in the accumulating sediment at the sole of the glacier. Under these conditions, the till either flowed away from the zone of release at the base of the glacier and (or) was being lightly smeared by a partially grounded glacier.
Textural map units in quartzo-feldspathic mylonitic rocks
Authors: Hanmer Simon
Published: June 2009

The classical macrotextural subdivision of quartzo-feldspathic mylonitic rocks yields only three rock types: protomylonite, mylonite, and ultramylonite. This restriction impedes detailed mapping of the internal textural transitions common in wide, deep-seated, crustal-scale shear zones, where such transitions may occur over kilometres and involve several clearly mappable textural types. The introduction of two objectively defined field mapping terms, "homoclastic" and "heteroclastic," describing the macroscopic grain-size distribution within the porphyroclast population provides descriptive flexibility without changing the matrix–porphyroclast basis of the established classification. This allows the description of textural paths other than protomylonite → mylonite → ultramylonite and facilitates the consideration of textural paths in terms of strain partitioning between the constituent grains of the deforming aggregate, rather than as a simple function of finite strain.
Lead isotopic fingerprinting of tectono-stratigraphic terranes, east-central Alaska
Authors: Aleinikoff John N. , Dusel-Bacon Cynthia , Foster Helen L. , Nokleberg Warren J.
Published: June 2009

Common lead isotopic compositions have been determined on feldspars from meta-igneous rocks from nine tectono-stratigraphic terranes or subterranes in east-central Alaska. Most of the terranes have distinct and well-defined signatures in terms of isotopic composition; thus, most can be distinguished on conventional lead isotopic diagrams. Lead isotopic ratios provide evidence for (1) possible sources for the igneous rocks, (2) time of metamorphism, (3) correlation of terrane fragments, and (4) delineation of juxtaposed terranes. Determination of lead isotopic ratios from igneous rocks can be useful in characterizing tectono-stratigraphic terranes (as to mantle or crustal origin) and in correlation, particularly where terrane relationships are enigmatic.
Fossil Coleoptera from the postglacial spruce–pine transition period near Minesing Swamp, Ontario
Authors: Miller Randall F. , Fitzgerald W. D. , Buhay D. N.
Published: June 2009

Analysis of Coleoptera fragments from a woody peat overlain by alluvial sands, near the margin of Minesing Swamp, records the adjustment of the beetle fauna to climatic change at the time of the spruce–pine transition. The site, dated at 10 280 years BP, contains a small but interesting insect assemblage recovered from a 1 m section. Bark beetles and staphylinid beetles typical of the Boreal forest occur in the spruce pollen zone. Higher in the section bark beetles are absent, and staphylinid beetles typical of the Great Lakes – St. Lawrence Forest Region occur in the pine and hemlock pollen zones.
TUNING MAGNETIC DISORDER IN DILUTED MAGNETIC SEMICONDUCTORS USING HIGH FIELDS TO 89 TESLA
Authors: CROOKER SCOTT A. , SAMARTH NITIN
Published: June 2009

We describe recent and ongoing studies at the National High Magnetic Field Laboratory at Los Alamos using the new "100 Tesla Multi-Shot Magnet", which is presently delivering fields up to ~89 T during its commissioning. We discuss the first experiments performed in this magnet system, wherein the linewidth of low-temperature photoluminescence spectra was used to directly reveal the degree of magnetic alloy disorder 'seen' by excitons in single Zn 0.80 Cd 0.22 Mn 0.08 Se quantum wells. The magnetic potential landscape in II-VI diluted magnetic semiconductors (DMS) is typically smoothed when the embedded Mn 2+ spins align in an applied field. However, an important (but heretofore untested) prediction of current models of compositional disorder is that magnetic alloy fluctuations in many DMS compounds should increase again in very large magnetic fields approaching 100 T. We observed precisely this increase above ~70 T, in agreement with a simple model of magnetic alloy disorder.
GRAPHENE IN THE QUANTUM HALL REGIME: EFFECTS OF VACANCIES, SUBLATTICE POLARIZATION AND DISORDER
Authors: PEREIRA ANA L. C. , SCHULZ PETER A.
Published: June 2009

We investigate the effects of vacancies, disorder and sublattice polarization on the electronic properties of a monolayer graphene in the quantum Hall regime. Energy spectra as a function of magnetic field and the localization properties of the states within the graphene Landau levels (LLs) are calculated through a tight-binding model. We first discuss our results considering vacancies in the lattice, where we show that vacancies introduce extra levels (or well-defined bands) between consecutive LLs. An striking consequence here is that extra Hall resistance plateaus are expected to emerge when an organized vacancy superlattice is considered. Secondly, we discuss the anomalous localization properties we have found for the lowest LL, where an increasing disorder is shown to enhance the wave functions delocalization (instead of inducing localization). This unexpected effect is shown to be directly related to the way disorder increasingly destroys the sublattice (valley) polarization of the states in the lowest LL. The reason why this anomalous disorder effect occurs only for the zero-energy LL is that, in absence of disorder, only for this level all the states are sublattice polarized, i.e., their wave functions have amplitudes in only one of the sublattices.
TRANSVERSE SPIN TRANSPORT IN GRAPHENE
Authors: MOHIUDDIN TARIQ M. G. , ZHUKOV A. A. , ELIAS D. C. , HILL E. W. , MOROZOV S.V. , GEIM A. K. , NOVOSELOV K. S.
Published: June 2009

In this paper we report transverse spin transport properties of graphene in a device, where for the first time a mono-atomically thin atomic fabric was sandwiched between magnetic thin films. We found that a single layer graphene flake was sufficient to break the exchange coupling between magnetic films and also to enhance the magnetoresistance effect.
LANDAU LEVEL SPECTROSCOPY OF DIRAC-LIKE FERMIONS IN MULTILAYER GRAPHENE
Authors: POTEMSKI M.
Published: June 2009

The results of spectroscopic (magneto-transmission and Raman scattering) studies1–8 of multilayers of carbon which are thermally decomposed from carbon-terminated surface of silicon carbide, and of thin layers of highly oriented pyrolytic and natural graphite were presented.

Those carbon multilayers on silicon carbide which are not directly affected by the SiC / C interface and which in consequence are nearly charge neutral show the magneto-optical properties identical with the properties characteristic of a single graphite sheet, graphene. Inter Landau level transitions in this multilayer graphene have been studied in a wide spectral range from far-infrared to almost visible region. The dispersion relations of electronic states are found to reflect the form of the Dirac cone with almost perfect electron-hole symmetry and only weak deviations from linearity at high energies. Cyclotron resonance transition in multilayer graphene can be observed in magnetic fields down to 40 mT, and its width is practically independent on temperature up to 300 K. Such parameters as carrier mobility and minimal conductivity as well as the possibility to probe the immediate vicinity of the Dirac point were evaluated and discussed in detail.

For comparison, the magneto-optical properties of thin layers of bulk graphite were also reported. The Dirac like electronic dispersion relations are also found in these systems, but only in the vicinity of the particular (H) point of the Brillouin zone. In general, the measured spectra are, however, more complex and reflect the three-dimensional character of graphene layers with Bernal stacking.

Note from Publisher: This article contains the abstract only.
NON-LINEAR TRANSPORT IN VERY HIGH LANDAU LEVELS OF TWO-DIMENSIONAL ELECTRON SYSTEMS
Authors: ZUDOV M. A. , CHIANG H.-S. , HATKE A. T. , ZHANG W. , PFEIFFER L. N. , WEST K. W.
Published: June 2009

We study magnetoresistivity oscillations induced by microwave radiation or acoustic phonons in high-mobility two-dimensional electron systems subject to dc electric field. In microwave-irradiated samples the response is governed by combined electron transitions, composed of microwave absorption and scattering off impurities. In non-irradiated samples, acoustic phonon resonances are tuned by dc electric field. Here, we show that in both experiments scattering off impurities without microwave or phonon absorption plays an important role and might even dominate the response.
BAND-LIMITED RADIATION SENSING USING THE RADIATION-INDUCED MAGNETO-RESISTANCE OSCILLATIONS
Authors: MANI R. G.
Published: June 2009

Tuned narrow-band-sensing of microwave and terahertz radiation can be realized by subjecting an irradiated two-dimensional electron system to both a static and a time varying magnetic field, and detecting at the harmonics of the modulation.
MAGNETIC FIELD INDUCED INSTABILITIES IN LOCALIZED TWO-DIMENSIONAL ELECTRON SYSTEMS
Authors: BAENNINGER MATTHIAS , GHOSH ARINDAM , PEPPER MICHAEL , BEERE HARVEY E. , FARRER IAN , RITCHIE DAVID A.
Published: June 2009

The results of extensive transport studies in localized regime of mesoscopic two-dimensional electron systems (2DES) with varying disorder are presented. A quick overview of previously achieved result is given. The main focus is on the observation of density dependent instabilities manifested by strong resistance oscillations induced by high perpendicular magnetic fields B⊥. While the amplitude of the oscillations is strongly enhanced with increasing B⊥, their position in electron density remains unaffected. The temperature dependence of resistivity shows a transition from an activated behaviour at high temperature to a saturated behaviour at low T. In the positions of resistance minima, the T dependence can even become metal-like (dρ/dT > 0). The activation energies obtained from the high T behaviour exhibit a formation of plateaux in connection with the resistance oscillations when analyzed as a function of electron density. We suggest the interplay between a strongly interacting electron phase and the background disorder as a possible explanation for our observation.
DISTORTION OF THE 2D WIGNER CRYSTAL INTO A 'QUASI-3D' INSULATOR
Authors: PIOT B. A. , DEAN C. R. , GERVAIS G. , JIANG Z. , ENGEL L. W. , PFEIFFER L. N. , WEST K. W.
Published: June 2009

Applying high magnetic fields parallel to the surface of a high-mobility 2D electron gas, we have recently observed a transition from the fractional quantum Hall liquid to an insulating phase, for filling factors as high as ν = 0.8 [B. A. Piot et al., Nature Phys. doi:10.1038/nphys1094]. This transition can be seen as a continuous distortion of the 2D Wigner crystal into a 'quasi-3D' insulating state. Here, we provide additional arguments confirming that carrier localization cannot be accounted for by disorder effects alone, and instead is most likely due to the stabilization of an electron solid by the strong parallel magnetic field in a 'quasi-3D' geometry.
SIGNATURES OF INHOMOGENEOUS ELECTRONIC STATE IN QUANTUM LIMIT IN GRAPHITE
Authors: KOPELEVICH YAKOV , DA SILVA ROBSON R.
Published: June 2009

In-plane magnetoresistance (MR) measurements performed on highly oriented pyrolytic graphite (HOPG) in Corbino-disk geometry revealed signatures of the electronic inhomogeneous state. In particular, the obtained results showed that besides of the Shubnikov-de-Haas (SdH) effect, the magnetic field B > 4 T triggers MR oscillations of a different origin that are spatially asymmetric. The possible coexistence of different electronic states in quantized magnetic field is discussed.
NUCLEAR-SPIN-BASED MEASUREMENTS OF QUANTUM HALL SYSTEMS
Authors: HIRAYAMA YOSHIRO
Published: June 2009

Nuclear magnetic resonance (NMR) is widely used in the physical, chemical, and biological sciences. However, conventional NMR techniques based on induction-detection have drawbacks of low-sensitivity and the need of a relatively large sample. It is not suitable to investigate single or double layers (or their nanostructure), which is essential in studying quantum Hall (QH) effects. In this presentation, I discussed a resistively-detected technique to overcome the low-sensitivity limitation of conventional NMR and its application to QH systems.

Resistively-detected nuclear-spin-based measurements rely on enhanced interactions between electron and nuclear spins at the degenerate point of different electron-spin states. For example, at the ν = 2/3 degenerate point in a AlGaAs / GaAs system,1–3 nuclear-spin polarization far beyond the thermal equilibrium is generated using current flow (dynamic nuclear-spin polarization). Moreover, nuclear-spin polarization can be detected as enhanced resistance, which is proportional to the magnetization, Mz, of nuclear spins.2 It should be stressed that the special states of ν = 2/3 are needed for dynamic nuclear-spin polarization and Mz detection, but we can apply NMR spectrum and nuclear-spin relaxation (T1 time) measurements for any state we want to estimate.

These nuclear-spin-based measurements were successfully applied to characterize QH systems, especially their electron-spin features, using single and double layer systems where characteristics are controlled electrically by the gate biases. For a single layer, we could clarify skyrmion,2 spin-polarization of composite fermion,4 and enhanced spin-orbit interactions in a strongly asymmetric confinement.5 Exciting phases, like a canted antiferromagnetic phase, were studied in a double layer QH system with a total filling factor of 2 (Refs. 6, 7). The low-frequency mode was sensitively detected by monitoring T1, reflecting correlated electron spin features.7 The clear observations of the characteristics, which are difficult to detect in conventional transport and optical measurements, make nuclear-spin-based measurement combined with resistance-detection a versatile and powerful tool for studying QH physics. Possible extensions of such measurements to semiconductor nanosystems were also discussed.

The experiments discussed here were mainly carried out at NTT Basic Research Laboratories in collaboration with K. Muraki, N. Kumada, K. Takashina, K. Hashimoto, S. Watanabe and G. Yusa.

Note from Publisher: This article contains the abstract only.
OPTICALLY INDUCED DYNAMIC NUCLEAR SPIN POLARIZATION IN QUANTUM HALL REGIME OBSERVED BY A TIME-RESOLVED KERR ROTATION
Authors: FUKUOKA DAISUKE , TANAKA NAOKI , OTO KENICHI , MURO KIYOFUMI , HIRAYAMA YOSHIRO , KUMADA NORIO , YAMAGUCHI HIROSHI
Published: June 2009

The dynamics between electron and nuclear spins in quantum Hall regime is investigated by a time-resolved Kerr rotation (TRKR) spectroscopy carried down in tilted-field geometry. The spin-flip energy varies almost linearly with the applied magnetic field under the nuclear spin depolarizing radio frequency field and the helicity modulation of circularly polarized pump, while the spin-flip energy obtained under a circularly polarized pump deviates from linearly behavior. This deviation is ascribed to the Overhauser shift due to dynamic nuclear spin polarization (DNP). The DNP depends markedly on the filling factor and present peaks at even filling factors. These results can be well explained by a simple model based on the detailed balance between electron and nuclear spins.
GENERAL OVERVIEW OVER INVESTIGATIONS ON LOW-DIMENSIONAL CARBON-BASED MATERIALS IN MAGNETIC FIELDS ABOVE 50 T
Authors: PORTUGALL OLIVER
Published: June 2009

Carbon nanotubes have been intensively investigated in pulsed magnetic fields, mainly to identify the effect of a magnetic flux along the tube axis on the energy band structure. Clear manifestations of the Ahoronov-Bohm effect have been observed in near-infrared absorption measurements on suspended tubes1 as well as in single-tube transport experiments.2 Subsequent studies have shed light on the excitonic nature of optical excitations3 and the magnetic-field induced optical activity of such excitons.4,5 Ongoing activities are focussing on the magnetic alignment dynamics of carbon nanotubes in liquid suspension which has the potential to provide valuable information on their magnetic susceptibility.

Experimental investigations on graphene in pulsed magnetic fields are far less advanced than those on carbon nanotubes. This is due to various experimental factors such as intrinsically short integration times for optical experiments and the destructive effect of electromagnetic perturbations on insufficiently screened transport samples. First results have nevertheless been obtained in both cases: Previous absorption measurements6 up to 32 T have been extended to higher fields thereby confirming the characteristic B1/2-dependence of energy levels. Transport measurements, on the other hand, have revealed extended plateaus in the two-terminal resistance of graphene.7

In this talk we gave a complete overview over recent and ongoing experimental investigations on carbon nanotubes and graphene in magnetic fields above 50 T. We referred to the work of several international collaborations including groups from Houston, Los Alamos, Berlin, Oxford, Tokyo, Dublin, Grenoble and Toulouse.

Note from Publisher: This article contains the abstract only.
OBSERVATIONS OF PARALLEL FIELD INDUCED REENTRANT QUANTUM HALL EFFECTS IN WIDE GaAs QUANTUM WELLS
Authors: LUHMAN D. R. , PAN W. , LU T. M. , TSUI D. C. , PFEIFFER L. N. , BALDWIN K. W. , WEST K. W.
Published: June 2009

We report the results of tilted magnetic field experiments on three high quality wide GaAs quantum wells, with particular emphasis on the N ≥ 1 Landau levels. With an increasing component of in-plane magnetic field, B∥, we observe reentrant behavior for the odd filling factor quantum Hall states. This reentrance is not explained within a single-particle energy level crossing scheme and may be related to the collapse of interlayer tunneling.
ELECTRICAL INJECTION AND OPTICAL READOUT OF SPIN STATES IN A SINGLE QUANTUM DOT
Authors: KÜMMELL T. , GHALI M. , HUANG J. , ARIANS R. , BACHER G. , WENISCH J. , BRUNNER K.
Published: June 2009

We demonstrate electrically driven spin injection into a single semiconductor quantum dot. Spin polarized electrons are transferred from a diluted magnetic semiconductor ( ZnMnSe ) into InAs quantum dots embedded into GaAs barriers. The spin information can be extracted directly from the polarization degree of the electroluminescence signal stemming from an individual quantum dot. By slightly modifying the device design, we demonstrate a concept to electrically charge the quantum dot by a spin polarized electron and present a simple way to probe this spin state optically.
TERAHERTZ MAGNETOSPECTROSCOPY OF HEAVILY-DOPED Si(P)
Authors: LEWIS R. A. , VICKERS R. E. M.
Published: June 2009

We demonstrate that lightly-doped Si ( P ) displays extremely sharp absorption lines – the narrowest yet reported for any impurity in natural Si . The Zeeman splitting of many of these lines in magnetic fields <10 T has been studied previously by a number of groups. In this paper we focus on the behavior of metastable states associated with conduction-band Landau levels. The use of a rather heavily doped sample and strong magnetic fields, up to 18 T, assists in the observation of these.
INTRABAND AUGER EFFECT IN QUANTUM DOT STRUCTURES
Authors: GEBHARD T. , UNTERRAINER K. , ALVARENGA D. , GUIMARAES P. S. S. , VILLAS-BOAS J. M. , PIRES M. P. , VIEIRA G. S. , SOUZA P. L.
Published: June 2009

Intraband photocurrent and absorption measurements were performed on InAs / InGaAlAs / InP quantum dot structures. To identify the optical transitions, theoretical calculations were performed and showed that the observed PC is generated by a bound to bound transition, where the final state is about 200 meV deep below the conduction band continuum. The reported results strongly suggest that an Auger process plays a fundamental role in generating the observed intraband photocurrent.
EUCLIDEAN ACTION AT TUNNELING IN MAGNETIC FIELD
Authors: LARKIN I. A. , UJEVIC SEBASTIAN , IVLEV B. I.
Published: June 2009

A state of an electron in a quantum wire or a thin film becomes metastable, when a static electric field is applied perpendicular to the wire direction or the film surface. The state decays via tunneling through the created potential barrier. An additionally applied magnetic field, perpendicular to the electric field, can increase the tunneling decay rate of an excited state by many orders of magnitude. This happens when the state in the wire or the film has a velocity perpendicular to the magnetic field. According to the cyclotron effect, the velocity rotates under the barrier and becomes more aligned with the direction of tunneling. This mechanism can be called cyclotron enhancement of tunneling.
EXCITATION OF CONDUCTION ELECTRON SPIN RESONANCE IN Si QUANTUM WELLS
Authors: JANTSCH WOLFGANG , HOCHREINER ASTRID , MALISSA HANS , WILAMOWSKI ZBYSZEK
Published: June 2009

The spin resonance of conduction electrons in a one-sided modulation doped quantum well in Si shows anomalies which we attribute to the microwave current induced Rashba field. We review results on the anisotropy of the lineshape, the amplitude and the temperature dependence which can be qualitatively explained in terms of this current-induced conduction electron spin resonance.
EDGE MAGNETOPLASMONS AND EDGE HELICON IN QUANTUM HALL REGIME AT NOT-TOO-LOW TEMPERATURES
Authors: BALEV O. G. , SILVA SANDERSON , STUDART NELSON
Published: June 2009

At not-too-low temperatures, ħωc ≫ kBT ≫ ħvg/2ℓ0 where vg is the group velocity of the edge states and ℓ0 the magnetic length, we obtain new edge magnetoplasmons (EMPs). For ν = 1(2) and very strong dissipation, we find that all EMPs are very strongly damped, due to the dissipative processes at the edge states, but a new weakly damped mode termed edge helicon. We also study the effect of metallic gate on the helicon spectrum. For ν = 4 we obtain fundamental modes of the n = 0, 1 Landau levels and their renormalization due to the Coulomb coupling and the effect of a metallic gate on them.
QUANTUM HALL FERROMAGNET IN A DOUBLE WELL WITH VANISHING g-FACTOR
Authors: ARMAS L. E. G. , GUSEV G. M. , LAMAS T. E. , BAKAROV A. K. , PORTAL J. C.
Published: June 2009

We have studied the quantum Hall effect in Al x Ga 1-x As -double well structure with vanishing g-factor. We determined the density-magnetic field ns - B diagrams for the longitudinal resistance Rxx. In spite of the fact that the ns - B diagram for conventional GaAs double wells shows a striking similarity with the theory, we observed the strong difference between these diagrams for double wells with vanishing g-factor. We argue that the electron-electron interaction is responsible for unusual behavior of the Landau levels in such a system.
VALLEY SPLITTING AND g-FACTOR IN AlAs QUANTUM WELLS
Authors: DUARTE C. A. , GUSEV G. M. , LAMAS T. E. , BAKAROV A. K. , PORTAL J.-C.
Published: June 2009

Here we present the results of magneto resistance measurements in tilted magnetic field and compare them with calculations. The comparison between calculated and measured spectra for the case of perpendicular fields enable us to estimate the dependence of the valley splitting as a function of the magnetic field and the total Landé g -factor (which is assumed to be independent of the magnetic field). Since both the exchange contribution to the Zeeman splitting as well as the valley splitting are properties associated with the 2D quantum confinement, they depend only on the perpendicular component of the magnetic field, while the bare Zeeman splitting depends on the total magnetic field. This information aided by the comparison between experimental and calculated gray scale maps permits to obtain separately the values of the exchange and the bare contribution to the g -factor.
EFFECTS OF IONIZED IMPURITIES ON BINDING AND RECOMBINATION OF POSITIVE AND NEGATIVE QUASI-TWO-DIMENSIONAL MAGNETO-TRIONS
Authors: WÓJS ARKADIUSZ , BRYJA LESZEK , POTEMSKI MAREK
Published: June 2009

Binding energies of negative and positive trions in high magnetic fields are compared. Simultaneous inclusion of several Landau levels and quantum well subbands in exact numerical diagonalization allowed quantitative description of the coupling between in-plane dynamics (governed by interplay of cyclotron quantization and Coulomb interactions) and single-particle excitations in the normal direction. Symmetric and asymmetric GaAs quantum wells of different widths were considered, as well as the effect of a possible binding of trions by sparse ionized impurities nearby the quantum well.
MAGNETIC FIELD DEPENDENCE OF MANY-BODY ENHANCED ELECTRON TUNNELLING THROUGH A QUANTUM DOT
Authors: LARKIN IVAN A. , VDOVIN E. E. , KHANIN YU. N. , HENINI M.
Published: June 2009

We consider many-body enhanced electron tunnelling through an InAs quantum dot in magnetic field applied perpendicular to the tunneling direction. Critical exponent of Fermi edge singularity in tunneling current is calculated as a function of magnetic field. We use lowest Landau level approximation for electrons in emitter and perform scattering matrix calculation in Born approximation. Results are compared with recent experiments.
EFFECT OF Mn IONS ON SPIN RELAXATION AND LIFE-TIME OF e-h COMPLEXES IN CdSe/ZnSe/ZnMnSe QUANTUM DOTS
Authors: CHERNENKO A. V. , BRICHKIN A. S. , KULAKOVSKII V. D. , SOBOLEV N. A. , IVANOV S. V.
Published: June 2009

Photoluminescence measurements on individual CdSe / ZnSe / ZnMnSe quantum dots in a magnetic field up to 11 T both parallel and perpendicular to the sample growth plane at 1.6 K reveal a qualitative difference between samples with different strength of the sp-d exchange interaction controlled by means of varying the thickness of the nonmagnetic ZnSe layer. The observed difference is related with the dependence of the non-radiative Mn assisted recombination and the spin relaxation on magnetic field and the strength of the exchange interaction.
1.4 eV - LUMINESCENCE BAND IN 6H-SIC: SYMMETRY OF THE ASSOCIATED DEFECT
Authors: WYSMOŁEK A. , STĘPNIEWSKI R. , WARDAK K. , BARANOWSKI J. , POTEMSKI M. , TYMICKI E. , GRASZA K.
Published: June 2009

Magneto- and piezo-spectroscopy of high quality bulk samples have been used to clarify the origin of the characteristic, V1, V2 and V3 luminescence lines observed in 6 H - SiC polytypes, correspondingly, at 1.433, 1.398, and 1.368 eV. The uniaxial stress, up to 500 MPa, was applied along [11-20] and [10-10] directions, perpendicular to the c -axis of the investigated 6 H - SiC crystals. Magnetic field was applied in different directions with respect to the c -axis. The obtained results allow us to analyze in detail the symmetry of the initial and final states responsible for the V2 emission line. This analysis leads to a conclusion which contradicts the existing identification of the defect responsible for this characteristic emission.
HIGH MAGNETIC FIELD IN THz PLASMA WAVE DETECTION BY HIGH ELECTRON MOBILITY TRANSISTORS
Authors: SAKOWICZ M. , ŁUSAKOWSKI J. , KARPIERZ K. , GRYNBERG M. , VALUSIS G.
Published: June 2009

The role of gated and ungated two dimensional (2D) electron plasma in THz detection by high electron mobility transistors (HEMTs) was investigated. THz response of GaAs / AlGaAs and GaN / AlGaN HEMTs was measured at 4.4K in quantizing magnetic fields with a simultaneous modulation of the gate voltage UGS. This allowed us to measure both the detection signal, S, and its derivative d S/ d UGS. Shubnikov - de-Haas oscillations (SdHO) of both S and d S/ d UGS were observed. A comparison of SdHO observed in detection and magnetoresistance measurements allows us to associate unambiguously SdHO in S and d S/ d UGS with the ungated and gated parts of the transistor channel, respectively. This allows us to conclude that the entire channel takes part in the detection process. Additionally, in the case of GaAlAs / GaAs HEMTs, a structure related to the cyclotron resonance transition was observed.
MEGAGAUSS MAGNETIC FIELDS IN SEMICONDUCTOR PHYSICS
Authors: VON ORTENBERG MICHAEL
Published: June 2009

A review of megagauss experiments using different kinds of field generator up to 1,000 T is given. The effiency of the single-turn coil, the electromagnetic and the explosive flux-compression, and finally the nearly steady-state long-pulse generators are presented. The basic feature of magnetic fields in semiconductor physics is related to the quantity of the magnetic length λ = (ħ/ eB )1/2 where ħ and e are natural constants with the usual meaning and B is the magnetic flux density. For B = 100 T we obtain λ = 2.56 nm . The parameter λ is a measure for the extension of the corresponding wavefunction of the charged particle and completely independent of the cyclotron mass. It should be noted that megagauss magnetic fields and nano structures have thus a natural correspondence: the magnetic length λ serves as a length measure in space in the nm-regime to be tuned by the external magnetic field. A second feature of megagauss fields is the generally extremely short pulse of field realization accompanied by a very high dB / dt . In this way the fields are "transient" and can be used to study the dynamics of the charge-carrier system. Also "eddy current"-effects can modify the system and manifest in new physical phenomena. Setup, performance and data analysis are demonstrated in different examples.
DESIGN OF DECOUPLED CLINICAL DECISION SUPPORT FOR SERVICE-ORIENTED ARCHITECTURES
Authors: WEBER-JAHNKE JENS
Published: June 2009

Computer-based clinical decision support (CDS) contributes to cost savings, increased patient safety and quality of medical care. Most existing CDS systems are stand-alone products (first generation) or part of complete electronic medical record packages (second generation). Experience shows that creating and maintaining CDS systems is expensive and requires effort that should be economized by sharing them among multiple users. It makes good economic sense to share CDS service installations among a larger set of client systems. The paradigm of a service-oriented architecture (SOA) embraces this idea of sharing distributed services. Some attempts making CDS services available to distributed health information systems exist. However, these approaches have not gained much adoption. We argue that they do not provide a sufficient level of decoupling between client and CDS in order to be broadly reusable in SOAs. In this paper, we present a new CDS service component called EGADSS, which has been designed and implemented with the declared objective to minimize the coupling between client and CDS server. We present our key design decisions, which are guided by empirical research in SOA development. We evaluate our result theoretically by measuring the level of decoupling achieved compared to existing CDS approaches. Furthermore, we report on an empirical evaluation of the resulting design, integrating the EGADSS service with an example client system.
A FRAMEWORK FOR TOOL-BASED SOFTWARE ARCHITECTURE RECONSTRUCTION
Authors: KANG SUNGWON , LEE SEONAH , LEE DANHYUNG
Published: June 2009

For software with nontrivial size and complexity, it is not feasible to manually perform architecture reconstruction. Therefore it is essential for the software architecture miner who is mining architecture from the existing software to have a well-defined software architecture reconstruction process that helps incorporate as much tool use as possible at the appropriate steps of architecture reconstruction. There are some existing software architecture reconstruction frameworks but they do not provide guidelines on how to systematically utilize tools to produce architecture views for a reconstruction purpose. In this paper, we propose a framework for tool-based software architecture reconstruction. This framework consists of a generic process for software architecture reconstruction and the steps to derive from it a concrete tool-based process to be used for actual architecture reconstruction. The architecture miner can use this framework to analyze source code for modifying source code as well as to reconstruct software architecture from source code.
VIBRO-ACOUSTIC ANALYSIS OF COMPOSITE CIRCULAR DISC WITH VARIOUS ORTHOTROPIC PROPERTIES
Authors: KUMAR BOORLE RAJESH , GANESAN N. , SETHURAMAN RAJU
Published: June 2009

Composite circular discs with polar orthotropic and rectangular orthotropic fibers of different composite materials are modeled and their vibration response due to harmonic point load was computed by finite element method (FEM) using ANSYS. Acoustic response of composite circular disc was computed by coupling the vibration data from FEM to the boundary element method using LMS SYSNOISE.
NONCONFORMING FINITE ELEMENT METHODS FOR THE THREE-DIMENSIONAL HELMHOLTZ EQUATION: ITERATIVE DOMAIN DECOMPOSITION OR GLOBAL SOLUTION?
Authors: GAUZELLINO PATRICIA M. , ZYSERMAN FABIO I. , SANTOS JUAN E.
Published: June 2009

Iterative domain decomposition (DD) nonconforming finite element methods for the Helmholtz equation attempt to solve two problems. First, there exists no efficient algorithms able to solve the large sparse linear system arising from the discretization of the equation via the standard finite elements method. Secondly, even when DD methods generally yield small matrices, standard conforming elements, such as Q1 elements, force the transmission of a relatively large amount of data among subdomains.

In this paper, we compared performance of global methods and a set of DD techniques to solve the Helmholtz equation in a three-dimensional domain. The efficiency of the algorithms is measured in terms of CPU time usage and memory requirements. The role of domain size and the linear solver type used to solve each local problem within each subdomain was also analyzed. The numerical results show that iterative DD methods perform far better than global methods. In addition, iterative DD methods involving small subdomains work better than those with subdomains involving a large number of elements. Properties of the iterative DD algorithms such as scalability, robustness, and parallel performance are also analyzed.
WAVELET ESTIMATORS FOR LONG MEMORY IN STOCK MARKETS
Authors: MABROUK ANOUAR BEN , KORTAS HEDI , AMMOU SAMIR BEN
Published: June 2009

In this paper, fractional integrating dynamics in the return and the volatility series of stock market indices are investigated. The investigation is conducted using wavelet ordinary least squares, wavelet weighted least squares and the approximate Maximum Likelihood estimator. It is shown that the long memory property in stock returns is approximately associated with emerging markets rather than developed ones while strong evidence of long range dependence is found for all volatility series. The relevance of the wavelet-based estimators, especially, the approximate Maximum Likelihood and the weighted least squares techniques is proved in terms of stability and estimation accuracy.
NEW NUMERICAL SCHEME FOR PRICING AMERICAN OPTION WITH REGIME-SWITCHING
Authors: KHALIQ A. Q. M. , LIU R. H.
Published: June 2009

This paper is concerned with regime-switching American option pricing. We develop new numerical schemes by extending the penalty method approach and by employing the θ-method. With regime-switching, American option prices satisfy a system of m free boundary value problems, where m is the number of regimes considered for the market. An (optimal) early exercise boundary is associated with each regime. Straightforward implementation of the θ-method would result in a system of nonlinear equations requiring a time-consuming iterative procedure at each time step. To avoid such complications, we implement an implicit approach by explicitly treating the nonlinear terms and/or the linear terms from other regimes, resulting in computationally efficient algorithms. We establish an upper bound condition for the time step size and prove that under the condition the implicit schemes satisfy a discrete version of the positivity constraint for American option values. We compare the implicit schemes with a tree model that generalizes the Cox-Ross-Rubinstein (CRR) binomial tree model, and with an analytical approximation solution for two-regime case due to Buffington and Elliott. Numerical examples demonstrate the accuracy and stability of the new implicit schemes.
CONVERGENCE SPEED OF GARCH OPTION PRICE TO DIFFUSION OPTION PRICE
Authors: DUAN JIN-CHUAN , WANG YAZHEN , ZOU JIAN
Published: June 2009

It is well known that as the time interval between two consecutive observations shrinks to zero, a properly constructed GARCH model will weakly converge to a bivariate diffusion. Naturally the European option price under the GARCH model will also converge to its bivariate diffusion counterpart. This paper investigates the convergence speed of the GARCH option price. We show that the European option prices under the two corresponding models are equal up to an order near the square root of the length of discrete time interval.
THE EVALUATION OF AMERICAN OPTION PRICES UNDER STOCHASTIC VOLATILITY AND JUMP-DIFFUSION DYNAMICS USING THE METHOD OF LINES
Authors: CHIARELLA CARL , KANG BODA , MEYER GUNTER H. , ZIOGAS ANDREW
Published: June 2009

This paper considers the problem of numerically evaluating American option prices when the dynamics of the underlying are driven by both stochastic volatility following the square root process of Heston [18], and by a Poisson jump process of the type originally introduced by Merton [25]. We develop a method of lines algorithm to evaluate the price as well as the delta and gamma of the option, thereby extending the method developed by Meyer [26] for the case of jump-diffusion dynamics. The accuracy of the method is tested against two numerical methods that directly solve the integro-partial differential pricing equation. The first is an extension to the jump-diffusion situation of the componentwise splitting method of Ikonen and Toivanen [21]. The second method is a Crank-Nicolson scheme that is solved using projected successive over relaxation and which is taken as the benchmark for the price. The relative efficiency of these methods for computing the American call option price, delta, gamma and free boundary is analysed. If one seeks an algorithm that gives not only the price but also the delta and gamma to the same level of accuracy for a given computational effort then the method of lines seems to perform best amongst the methods considered.
HEDGE FUND PERFORMANCE: SOURCES AND MEASURES
Authors: EBERLEIN ERNST , MADAN DILIP B.
Published: June 2009

The concept of the gamma of a financed return as the highest level of stress that a return distribution can withstand is introduced. Stress is measured by positive expectation under a concave distortion of the return distribution accessed. Four distortions introduced in Cherny and Madan (2008) are employed in studying the distribution of returns available in the hedge fund universe. It is shown that the skewness, peakedness and tailweightedness of the standardized investment return significantly affects the Sharpe ratios required to reach a target gamma level.
SENSITIVITY ANALYSIS AND DENSITY ESTIMATION FOR THE HOBSON-ROGERS STOCHASTIC VOLATILITY MODEL
Authors: KAWAI REIICHIRO
Published: June 2009

Monte Carlo estimators of sensitivity indices and the marginal density of the price dynamics are derived for the Hobson-Rogers stochastic volatility model. Our approach is based mainly upon the Kolmogorov backward equation by making full use of the Markovian property of the dynamics given the past information. Some numerical examples are presented with a GARCH-like volatility function and its extension to illustrate the effectiveness of our formulae together with a clear exhibition of the skewness and the heavy tails of the price dynamics.
Acoustic sensor network design for position estimation
Authors: Cevher Volkan , Kaplan Lance M.
Published: June 2009

In this article, we develop tractable mathematical models and approximate solution algorithms for a class of integer optimization problems with probabilistic and deterministic constraints, with applications to the design of distributed sensor networks that have limited connectivity. For a given deployment region size, we calculate the Pareto frontier of the sensor network utility at the desired probabilities for
d
-connectivity and
k
-coverage. As a result of our analysis, we determine (1) the number of sensors of different types to deploy from a sensor pool, which offers a cost vs. performance trade-off for each type of sensor, (2) the minimum required radio transmission ranges of the sensors to ensure connectivity, and (3) the lifetime of the sensor network. For generality, we consider randomly deployed sensor networks and formulate constrained optimization technique to obtain the localization performance. The approach is guided and validated using an unattended acoustic sensor network design. Finally, approximations of the complete statistical characterization of the acoustic sensor networks are given, which enable average network performance predictions of any combination of acoustic sensors.
Design, implementation, and evaluation of EnviroMic
Authors: Luo Liqian , Cao Qing , Huang Chengdu , Wang Lili , Abdelzaher Tarek F. , Stankovic John A. , Ward Michael
Published: June 2009

This article presents the design, implementation, and evaluation of
EnviroMic
, a low-cost experimental prototype of a novel distributed acoustic monitoring, storage, and trace retrieval system designed for disconnected operation. Our intended use of acoustic monitoring is to study animal populations in the wild. Since a permanent connection to the outside world is not assumed and due to the relatively large size of audio traces, the system must optimally exploit available resources such as energy and network storage capacity. Towards that end, we design, prototype, and evaluate distributed algorithms for coordinating acoustic recording tasks, reducing redundancy of data stored by nearby sensors, filtering out silence, and balancing storage utilization in the network. For experimentation purposes, we implement EnviroMic on a TinyOS-based platform and systematically evaluate its performance through both indoor testbed experiments and an outdoor deployment. Results demonstrate up to a four-fold improvement in effective storage capacity of the network compared to uncoordinated recording.
Optimal placement of distributed sensors against moving targets
Authors: Wettergren Thomas A. , Costa Russell
Published: June 2009

This article addresses the problem of deploying a sparse network of sensors for surveillance of moving targets. The sensor networks of interest consist of sensors which perform independent binary detection on a target, and report detections to a central node for fusion. An optimization framework is developed for placement of sensors within a bounded search region, given sensor performance characteristics, prior information on anticipated target characteristics, and a distributed detection criteria. Individual sensor performance is represented parametrically as are priors on target dynamics. Several numerical examples are included that illustrate the utility of the optimization approach.