bluuebunny/crossref_metadata_2025 huggingface dataset:
Mean thermal structure of the low‐latitude middle atmosphere studied using Gadanki Rayleigh lidar, Rocket, and SABER/TIMED observations
Authors: Kishore Kumar G. , Venkat Ratnam M. , Patra A. K. , Vijaya Bhaskara Rao S. , Russell James
Published: December 2008

The present study delineates the low‐latitude thermal structure in the altitude range of 30 to 110 km using Gadanki (13.5°N, 79.2°E) Rayleigh lidar (1998–2007), Thumba (8.5°N,77°E) rocketsondes (1970–1991), and SABER/TIMED satellite (2002–2007) observations. This study particularly addresses whether (1) the lidar data available only during nighttime is sufficient to study the background mean thermal structure in 30–80 km altitude region, (2) the nonavailability of the lidar data during cloudy seasons (monsoon) will affect the derived background mean thermal structure, and (3) any alternate satellite observations can be used for getting the thermal structure of the middle atmosphere. The comparisons between temperatures measured by Rayleigh lidar and SABER show good agreement, suggesting that SABER data can be used effectively to study the mean thermal structure. The nocturnal average and diurnal average of temperature from SABER show similar features, suggesting that data available from lidar only during nighttime can be effectively used to study the mean background thermal structure between 30 and 80 km. Large difference between SABER and lidar observations during monsoon suggests that low data rate available from the lidar is not sufficient to obtain the mean thermal structure during cloudy seasons. Beside this, variations in stratopause (mesopause) height and temperature are also studied. The stratopause and mesopause lie in the height region of 47–49 km and 97–99 km, with peak temperature of 265 K and 170 K, respectively. Stratopause height and temperature show clear semiannual oscillation. No significant seasonal variation is observed either in mesopause height or in temperature at this low latitude.
Long‐range transport and vertical structure of Asian dust from CALIPSO and surface measurements during PACDEX
Authors: Huang Jianping , Minnis Patrick , Chen Bin , Huang Zhongwei , Liu Zhaoyan , Zhao Qingyun , Yi Yuhong , Ayers J. Kirk
Published: December 2008

Knowledge of long‐range transport and vertical distribution of Asian dust aerosols in the free troposphere is important for estimating their impact on climate. Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), surface micropulse lidar (MPL), and standard surface measurements are used to directly observe the long‐range transport and vertical distribution of Asian dust aerosols in the free troposphere during the Pacific Dust Experiment (PACDEX). The MPL measurements were made at the Loess Plateau (35.95°N, 104.1°E) near the major dust source regions of the Taklamakan and Gobi deserts. Dust events are more frequent in the Taklamakan, where floating dust dominates, while more intensive, less frequent dust storms are more common in the Gobi region. The vertical distribution of the CALIPSO backscattering/depolarization ratios indicate that nonspherically shaped dust aerosols floated from near the ground to an altitude of approximately 9 km around the source regions. This suggests the possible long‐range transport of entrained dust aerosols via upper tropospheric westerly jets. A very distinct large depolarization layer was also identified between 8 and 10 km over eastern China and the western Pacific Ocean corresponding to dust aerosols transported from the Taklamakan and Gobi areas, as confirmed by back trajectory analyses. The combination of these dust sources results in a two‐layer or multilayered dust structure over eastern China and the western Pacific Ocean.
Geodynamic evolution of the SW Variscides: Orogenic collapse shown by new tectonometamorphic and isotopic data from western Ossa‐Morena Zone, SW Iberia
Authors: Rosas F. M. , Marques F. O. , Ballèvre M. , Tassinari C.
Published: December 2008

The pre‐Mesozoic geodynamic evolution of SW Iberia has been investigated on the basis of detailed structural analysis, isotope dating, and petrologic study of high‐pressure (HP) rocks, revealing the superposition of several tectonometamorphic events: (1) An HP event older than circa 358 Ma is recorded in basic rocks preserved inside marbles, which suggests subduction of a continental margin. The deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments. The sense of shear is top to south, revealing thrusting synthetic with subduction (underthrusting) to the north. (2) Recrystallization before circa 358 Ma is due to a regional‐scale thermal episode and magmatism. (3) Noncoaxial deformation with top to north sense of shear in northward dipping large‐scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies. This indicates exhumation by normal faulting in a detachment zone confined to the top to north and north dipping shear zones during postorogenic collapse soon after 358 Ma ago (inversion of earlier top to south thrusts). (4) Static recrystallization at circa 318 Ma is due to regional‐scale granitic intrusions.
Effects of Cerebral Ischemia on Neuronal Hemoglobin
Authors: He Yangdong , Hua Ya , Liu Wenquan , Hu Haitao , Keep Richard F , Xi Guohua
Published: December 2008

This study examined whether neuronal hemoglobin (Hb) is present in rats. It then examined whether cerebral ischemia or ischemic preconditioning (IPC) affects neuronal Hb levels in vivo and in vitro. In vivo, male Sprague-Dawley rats were subjected to either 15 mins of transient middle cerebral artery occlusion (MCAO) with 24 h of reperfusion, an IPC stimulus, or 24 h of permanent MCAO (pMCAO), or IPC followed 3 days later by 24 h of pMCAO. In vitro, primary cultured neurons were exposed to 2 h of oxygen—glucose deprivation (OGD) with 22 h of reoxygenation. Results showed that Hb is widely expressed in rat cerebral neurons but not astrocytes. Hemoglobin expression was significantly upregulated in the ipsilateral caudate and the cortical core of the middle cerebral artery territory after IPC. Hemoglobin levels also increased more in the penumbral cortex and the contralateral hemisphere 24 h after pMCAO, but expressions in the ipsilateral caudate and the cortical core area were decreased. Ischemic preconditioning modified pMCAO-induced brain Hb changes. Neuronal Hb levels in vitro were increased by 2 h of OGD and 22 h of reoxygenation. These results indicate that Hb is synthesized in neurons and can be upregulated by ischemia.
Behavioral and Psychiatric Genetics: Learning from History
Authors: Schaffner Kenneth
Published: December 2008

Behavioral and Psychiatric Genetics (BPG) offers great promise for clarifying the causes of both normal behaviors as well as psychiatric disorders, and in the latter case serving as a more rational basis for treatments. But the field has also generated serious social concerns about individual and ethnic stereotyping of intelligence and violent behaviors. This short talk identifies some of these themes from the 1970s, 80s, and 90s, and reviews recent shifts about the directions BPG is taking in the first decade of the twenty-first century. I cover the collapse of simple molecular gene-behavior models in the 1990s, and the rise of gene-environment interaction paradigms, as well as the increasing role of neuroscience in BPG in the present decade. I close by citing molecular-studies that may require we revisit previous historical lessons, now in a molecular genetics-neuroscience context.To watch Dr. Schaffner’s presentation, please see the "Google Video posting.":http://video.google.com/videoplay?docid=-2384504189343195854&hl=en
Ready, set, internalize: mechanisms and regulation of GLUT4 endocytosis
Authors: Antonescu Costin N. , Foti Michelangelo , Sauvonnet Nathalie , Klip Amira
Published: December 2008

The facilitative glucose transporter GLUT4, a recycling membrane protein, is required for dietary glucose uptake into muscle and fat cells. GLUT4 is also responsible for the increased glucose uptake by myofibres during muscle contraction. Defects in GLUT4 membrane traffic contribute to loss of insulin-stimulated glucose uptake in insulin resistance and Type 2 diabetes. Numerous studies have analysed the intracellular membrane compartments occupied by GLUT4 and the mechanisms by which insulin regulates GLUT4 exocytosis. However, until recently, GLUT4 internalization was less well understood. In the present paper, we review: (i) evidence supporting the co-existence of clathrin-dependent and independent GLUT4 internalization in adipocytes and muscle cells; (ii) the contrasting regulation of GLUT4 internalization by insulin in these cells; and (iii) evidence suggesting regulation of GLUT4 endocytosis in muscle cells by signals associated with muscle contraction.
Equation of state and high pressure properties of a fluorinated terpolymer: THV 500
Authors: Dattelbaum Dana M. , Sheffield Stephen A. , Stahl David , Weinberg Michael , (Kit) Neel Christopher , Thadhani Naresh
Published: December 2008

We present the results of an investigation of the static compressive and dynamic (shock) responses of a fluorinated terpolymer of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (Dyneon THV 500), in an effort to further understand its behavior under static and dynamic high pressures, and elucidate its equation of state properties. Fluorinated polymers, and, in particular, their copolymers, have garnered increasing attention by the static high pressure and shock wave communities, due to their widespread use in engineering applications, and formulation into energetic materials as binders. Shock wave compression experiments performed at two laboratories showed good consistency, and provide the first Hugoniot data for this fluorinated terpolymer. The Hugoniot of THV 500 is in general agreement with that of the related fluoropolymers polytetrafluoroethylene and poly(chlorotrifluoroethylene-co-vinylidene fluoride), reported previously. The static compressive data, combined with measurement of the ambient pressure thermodynamic parameters, have been used to formulate an equation of state based on the Helmholtz free energy, which was shown to adequately represent the dynamic response of the polymer to ∼5 GPa.
Assessing the dephasing dynamics of water from linear field-resolved pulse propagation experiments and simulations in highly absorbing solutions
Authors: Gruetzmacher Julie A. , Nome Rene A. , Moran Andrew M. , Scherer Norbert F.
Published: December 2008

We measure and simulate electric field distortions resulting from propagation of mid-infrared pulses that are resonant with the OH stretch vibration through optically dense HDO:D2O. These distortions are characterized experimentally by full-field-resolved time- and frequency-domain measurements, specifically cross-correlation frequency-resolved optical gating and spectral interferometry, establishing amplitude and phase of the signal fields. Correlation-function finite-difference time-domain (CF-FDTD) simulations using response functions for the OH-stretching vibration, obtained from nonlinear spectroscopic studies reported by others, show that details of the line shape functions are manifested in the measured (linear-response) spectrograms. The degree of homogeneous or inhomogeneous broadening present in the various model correlation functions is readily apparent in the measured and simulated signals. Surprisingly, the published correlation functions are shown to range from modest inhomogeneous to homogeneous line broadening. The present experimental and simulation approach is very useful for establishing the correct form of energy gap correlation functions and dephasing dynamics of IR and optical transitions. In the case of HDO:D2O, correlation functions with modest inhomogeneous broadening better reflect our measured responses.
Atypical micellization of star-block copolymer solutions
Authors: Chou Shih-Hao , Tsao Heng-Kwong , Sheng Yu-Jane
Published: December 2008

The self-assembly of star-block copolymer (ByAx)n in a selective solvent for its outer block is studied by using dissipative particle dynamics, where (ByAx)n denotes a n-armed star with each arm comprising of y solvophobic B-segments and x solvophilic A-segments. The effects of arm number, arm length, block length ratio y∕x, solvent quality, and component compatibility on mean aggregation number ⟨p⟩ are examined. Unusual micellization behaviors are observed. The total number of arms in a multimolecular micelle n* is invariant with the arm number but grows with the segment concentration φ, which is different from typical micellization of short-chain surfactants. For a given φ, multimolecular micelles are formed for stars with n<n*(φ) and the mean aggregation number follows ⟨p⟩=n*∕n. As n⩾n*, only unimolecular micelles exist in the solution. According to the n*-φ relation, the critical multimolecular micelle concentration is found to grow linearly with arm number. As solvent quality deteriorates or component compatibility increases, the total arm number within a micelle rises.
Relativistic calculation of nuclear magnetic shielding tensor using the regular approximation to the normalized elimination of the small component. III. Introduction of gauge-including atomic orbitals and a finite-size nuclear model
Authors: Hamaya S. , Maeda H. , Funaki M. , Fukui H.
Published: December 2008

The relativistic calculation of nuclear magnetic shielding tensors in hydrogen halides is performed using the second-order regular approximation to the normalized elimination of the small component (SORA-NESC) method with the inclusion of the perturbation terms from the metric operator. This computational scheme is denoted as SORA-Met. The SORA-Met calculation yields anisotropies, Δσ=σ∥−σ⊥, for the halogen nuclei in hydrogen halides that are too small. In the NESC theory, the small component of the spinor is combined to the large component via the operator σ⃗⋅π⃗U/2c, in which π⃗=p⃗+A⃗, U is a nonunitary transformation operator, and c≅137.036 a.u. is the velocity of light. The operator U depends on the vector potential A⃗ (i.e., the magnetic perturbations in the system) with the leading order c−2 and the magnetic perturbation terms of U contribute to the Hamiltonian and metric operators of the system in the leading order c−4. It is shown that the small Δσ for halogen nuclei found in our previous studies is related to the neglect of the U(0,1) perturbation operator of U, which is independent of the external magnetic field and of the first order with respect to the nuclear magnetic dipole moment. Introduction of gauge-including atomic orbitals and a finite-size nuclear model is also discussed.
Rotationally resolved studies of S and the exciton coupled S1/S2 origin regions of diphenylmethane and the d12 isotopologue
Authors: Stearns Jaime A. , Pillsbury Nathan R. , Douglass Kevin O. , Müller Christian W. , Zwier Timothy S. , Plusquellic David F.
Published: December 2008

Rotationally resolved microwave and ultraviolet spectra of jet-cooled diphenylmethane (DPM) and DPM-d12 have been obtained in S0, S1, and S2 electronic states using Fourier-transform microwave and UV laser/molecular beam spectrometers. The S0 and S1 states of both isotopologues have been well fit to asymmetric rotor Hamiltonians that include only Watson distortion parameters. The transition dipole moment (TDM) orientations of DPM and DPM-d12 are perpendicular to the C2 symmetry axes with 66(2)%:34(2)% a:c hybrid-type character, establishing the lower exciton S1 origin as a completely delocalized, antisymmetric combination of the zero-order locally excited states of the toluene-like chromophores. In contrast, the rotational structures of the S2 origin bands at S1+123 cm−1 and S1+116 cm−1, respectively, display b-type Q-branch transitions and lack the central a-type Q-branch features that characterize the S1 origins, indicating TDM orientations parallel to the C2(b) symmetry axes as anticipated for the upper exciton levels. However, rotational fits were not possible in line with expectations from previous work [N. R. Pillsbury, J. A. Stearns, C. W. Müller, T. S. Zwier, and D. F. Plusquellic, J. Chem. Phys. 129, 114301 (2008)] where the S2 origins were found to be largely perturbed through vibronic interactions with the S1 symmetric, antisymmetric torsional, and butterfly levels in close proximity. Predictions from a dipole-dipole coupling model and ab initio theories are shown to be in fair agreement with the observed TDM orientations and exciton splitting. The need to include out-of-ring-plane dipole coupling terms indicates that in-plane models are not sufficient to fully account for the excitonic interactions in this bichromophore.
Spatiotemporal system reconstruction using Fourier spectral operators and structure selection techniques
Authors: Xu Daolin , Khanmohamadi Omid
Published: December 2008

A technique based on trigonometric spectral methods and structure selection is proposed for the reconstruction, from observed time series, of spatiotemporal systems governed by nonlinear partial differential equations of polynomial type with terms of arbitrary derivative order and nonlinearity degree. The system identification using Fourier spectral differentiation operators in conjunction with a structure selection procedure leads to a parsimonious model of the original system by detecting and eliminating the redundant parameters using orthogonal decomposition of the state data. Implementation of the technique is exemplified for a highly stiff reaction-diffusion system governed by the Kuramoto–Sivashinsky equation. Numerical experiments demonstrate the superior performance of the proposed technique in terms of accuracy as well as robustness, even with smaller sets of sampling data.
Universal serial bus powered and controlled isolated constant-current physiological stimulator
Authors: Holcomb Mark R. , Bekele Robel Y. , Lima Eduardo A. , Wikswo John P.
Published: December 2008

We have developed a compact, isolated, physiological, constant-current stimulator that is powered and controlled by a universal serial bus (USB) interface. The stimulator is designed to be used in ex vivo cardiac experiments but is suitable for a wide variety of settings. The cost and features compare very favorably with commercial stimulators usually used in research and student laboratories. In addition to being USB powered, other novel aspects of our stimulator include the ability to produce large currents, up to 100 mA through a typical 1 kΩ load, by means of a single high-voltage dc-to-dc converter; user-specified variable period, magnitude, and duration of complex monophasic or biphasic sequences; and easy integration via hardware or software into existing experimental setups.
High pressure structural and elastic properties of NiO up to 67 GPa
Authors: Liu L. , Li X. D. , Liu J. , Jiang S. , Li Y. C. , Shen G. Y. , Mao H. K. , Bi Y. , Xu J.
Published: December 2008

Using argon as the pressure medium, the structural and elastic properties of NiO have been investigated up to 67 GPa by the in situ synchrotron x-ray diffraction in a diamond anvil cell. Up to 67 GPa, NiO remains in the rhombohedral distorted rocksalt structure without phase transition. The lattice parameters of a and c, indexed in the hexagonal lattice, were found to decrease monotonically with increasing pressure, while the c/a ratio remains almost constant. The elastic properties of NiO were studied by analyzing the linewidth of various diffraction perks, which indicates that the factor S=(S11−S12−S44/2) is negative although the single-crystal elastic compliances S11 is positive, respectively, in the investigated pressure range.
Resistance switching of Au-implanted-ZrO2 film for nonvolatile memory application
Authors: Liu Qi , Guan Weihua , Long Shibing , Liu Ming , Zhang Sen , Wang Qin , Chen Junning
Published: December 2008

The resistive switching characteristics and switching mechanisms of the Au-implanted-ZrO2 film are extensively investigated for nonvolatile memory applications. Reversible resistance-switching behavior from a high resistance to low resistance state can be traced by dc voltage and pulse voltage. After more than 200 dc switching cycles, the resistance ratio between the high and low resistance states is more than 180 times under 0.7 V readout bias. In the voltage pulse test, the “write” and “erase” speeds can be as fast as 50 and 100 ns, respectively. No data loss is observed for more than 106 s. The formation and rupture of conducting filamentary paths related to the implanted Au ions are suggested to be responsible for the resistive switching phenomenon. The dependence of resistance on temperature indicates that the variable-range hopping conduction mechanism is dominated in the low-resistance state, while the current characteristics are governed by the trap-controlled space limited conduction mechanism in the high-resistance state.
A combined experimental/theoretical investigation of the near-infrared photodissociation of IBr−(CO2)n
Authors: Thompson Matthew A. , Martin Joshua P. , Darr Joshua P. , Lineberger W. Carl , Parson Robert
Published: December 2008

We report the collaborative experimental and theoretical study of the time-resolved recombination dynamics of photodissociated IBr−(CO2)n clusters. Excitation of the bare anionic chromophore to the dissociative A′ Π21/2 state yields only I− and Br products. Interestingly, however, the addition of a few solvent molecules promotes recombination of the dissociating chromophore on the X Σ21/2+ ground state, which correlates asymptotically with Br− and I products. This process is studied experimentally using time-resolved, pump-probe techniques and theoretically via nonadiabatic molecular dynamics simulations. In sharp contrast to previous I2− studies where more kinetic energy was released to the photofragments, the observed recombination times increase from picoseconds to nanoseconds with increasing cluster size up to n=10. The recombination times then drop dramatically back to picoseconds for cluster sizes n=11–14. This trend, seen both in experiment and theory, is explained by the presence of a solvent-induced well on the A′ state, the depth of which directly corresponds to the asymmetry of the solvation about the chromophore. The results seen for both the branching ratios and recombination times from experiment and theory show good qualitative agreement.
Determining electron temperature for small spherical probes from network analyzer measurements of complex impedance
Authors: Walker D. N. , Fernsler R. F. , Blackwell D. D. , Amatucci W. E.
Published: December 2008

In earlier work, using a network analyzer, it was shown that collisionless resistance (CR) exists in the sheath of a spherical probe when driven by a small rf signal. The CR is inversely proportional to the plasma density gradient at the location where the applied angular frequency equals the plasma frequency ωpe. Recently, efforts have concentrated on a study of the low-to-intermediate frequency response of the probe to the rf signal. At sufficiently low frequencies, the CR is beyond cutoff, i.e., below the plasma frequency at the surface of the probe. Since the electron density at the probe surface decreases as a function of applied (negative) bias, the CR will extend to lower frequencies as the magnitude of negative bias increases. Therefore to eliminate both CR and ion current contributions, the frequencies presently being considered are much greater than the ion plasma frequency, ωpi, but less than the plasma frequency, ωpe(r0), where r0 is the probe radius. It is shown that, in this frequency regime, the complex impedance measurements made with a network analyzer can be used to determine electron temperature. An overview of the theory is presented along with comparisons to data sets made using three stainless steel spherical probes of different sizes in different experimental environments and different plasma parameter regimes. The temperature measurements made by this method are compared to those made by conventional Langmuir probe sweeps; the method shown here requires no curve fitting as is the usual procedure with Langmuir probes when a Maxwell-Boltzmann electron distribution is assumed. The new method requires, however, a solution of the Poisson equation to determine the approximate sheath dimensions and integrals to determine approximate plasma and sheath inductances. The solution relies on the calculation of impedance for a spherical probe immersed in a collisionless plasma and is based on a simple circuit analogy for the plasma. Finally, the temperatures obtained using this method show reasonable agreement with those obtained using a conventional Langmuir sweep analysis of the spheres.
Structural changes and preferential cage occupancy of ethane hydrate and methane-ethane mixed gas hydrate under very high pressure
Authors: Hirai Hisako , Takahara Naoya , Kawamura Taro , Yamamoto Yoshitaka , Yagi Takehiko
Published: December 2008

High-pressure experiments of ethane hydrate and methane-ethane mixed hydrates with five compositions were performed using a diamond anvil cell in a pressure range of 0.1–2.8 GPa at room temperature. X-ray diffractometry and Raman spectroscopy showed structural changes as follows. The initial structure, structure I (sI), of ethane hydrate was retained up to 2.1 GPa without any structural change. For the mixed hydrates, sI was widely distributed throughout the region examined except for the methane-rich and lower pressure regions. For the ethane-rich and intermediate composition regions (73 mol % ethane sample and 53% sample), sI was maintained up to 2.1 GPa. With increasing methane component (34% and 30% samples), sI existed at pressures from 0.1 to about 1.0 GPa. Hexagonal structure (sH) appeared in addition to sI at 1.3 GPa for the 34% sample and at 1.1 GPa for the 30% sample. By further increasing the methane component (22% sample), structure II (sII) existed solely up to 0.3 GPa. From 0.3 to 0.6 GPa, sII and sI coexisted, and from 0.6 to 1.0 GPa only sI existed. At 1.2 GPa sH appeared, and sH and sI coexisted up to 2.1 GPa. Above 2.1 GPa, ethane hydrate and all of the mixed hydrates decomposed into ice VI and ethane fluid or methane-ethane fluid, respectively. The Raman study revealed that occupation of the small cages by ethane molecules occurred above 0.1 GPa in ethane hydrate and continued up to decomposition at 2.1 GPa, although it is thought that ethane molecules are contained only in the large cage.
Statistics and kinetics of single-molecule electron transfer dynamics in complex environments: A simulation model study
Authors: Paula Luciana C. , Wang Jin , Leite Vitor B. P.
Published: December 2008

Dynamics of the environments of complex systems such as biomolecules, polar solvents, and glass plays an important role in controlling electron transfer reactions. The kinetics is determined by the nature of a complex multidimensional landscape. By quantifying the mean and high-order statistics of the first-passage time and the associated ratios, the dynamics in electron transfer reactions controlled by the environments can be revealed. We consider real experimental conditions with finite observation time windows. At high temperatures, exponential kinetics is observed and there are multiple kinetic paths leading to the product state. At and below an intermediate temperature, nonexponential kinetics starts to appear, revealing the nature of the distribution of local traps on the landscape. Discrete kinetic paths emerge. At very low temperatures, nonexponential kinetics continues to be observed. We point out that the size of the observational time window is crucial in revealing the intrinsic nature of the real kinetics. The mean first-passage time is defined as a characteristic time. Only when the observational time window is significantly larger than this characteristic time does one have the opportunity to collect enough statistics to capture rare statistical fluctuations and characterize the kinetics accurately.
Power dissipation spectra and terahertz intervalley transfer gain in bulk GaAs under high electric fields
Authors: Zhu Y. M. , Unuma T. , Shibata K. , Hirakawa K. , Ino Y. , Kuwata-Gonokami M.
Published: December 2008

We have investigated terahertz radiation emitted from electrons photoexcited by femtosecond laser pulses in bulk GaAs under strong bias electric fields. Power dissipation spectra of electrons for step-function-like input electric fields have been obtained by calculating Fourier spectra of the measured terahertz traces. The cutoff frequency νc for negative power dissipation (i.e., gain) due to intervalley transfer is found to gradually increase with increasing electric fields below 50 kV/cm and saturate at ∼1 THz above 50 kV/cm at 300 K. From the temperature dependence of νc, it is found that νc is governed by the emission of optical phonons.
Dark current and band profiles in low defect density thick multilayered GaAs/InAs self-assembled quantum dot structures for infrared detectors
Authors: Asano Tetsuya , Madhukar Anupam , Mahalingam Krishnamurthy , Brown Gail J.
Published: December 2008

We report results of a systematic study of the structural and photoresponse properties of GaAs/{InAs quantum dot (QD)/InGaAs quantum well/GaAs} ×m multiple quantum dot (MQD) structures with m from 1 to 20 placed in n-GaAs/i(MQD)/n-GaAs configuration to act as quantum dot infrared photodetectors (QDIPs). Extremely low dislocation densities inferred from cross-sectional and plan-view transmission electron microscopy and the observed linear increase in photoluminescence intensity with MQD thickness reveal the high quality of these QDIP structures. Temperature and bias dependent dark and photocurrent measurements reveal dark current activation energies (Ea) increasing with the number of QD layers in a manner that indicates that Ea represents the built-in potential in the MQD region. These studies indicate the need for more quantitative modeling to guide optimal doping strategies and profiles to realize high photocurrents while maintaining acceptable dark current.
The effect of aluminum oxide incorporation on the material and electrical properties of hafnium oxide on Ge
Authors: Sawkar-Mathur Monica , Perng Ya-Chuan , Lu Jun , Blom Hans-Olof , Bargar John , Chang Jane P.
Published: December 2008

Hafnium aluminate thin films were synthesized by atomic layer deposition (ALD) to assess the effect of aluminum oxide incorporation on the dielectric/Ge interfacial properties. In these HfxAlyOz thin films, the Hf to Al cation ratio was effectively controlled by changing the ratio of hafnium oxide to aluminum oxide ALD cycles, while their short range order was changed upon increasing aluminum oxide incorporation, as observed by extended x-ray absorption fine structure analysis. The incorporation of aluminum oxide was shown to improve the electrical characteristics of hafnium oxide/Ge devices, including lower interface state densities and leakage current densities.
Spin precession induced by an effective magnetic field in a two-dimensional electron gas
Authors: Liu Genhua , Chen Yonghai , Jia Caihong , Wang Zhanguo
Published: December 2008

We theoretically study the spatial behaviors of the spin precession in a two-dimensional electron system with spin-orbit interaction. Through analysis of interaction between the spin and the effective magnetic field in the system, we obtain the general conditions to generate a persistent spin helix and predict a persistent spin helix pattern in [001]-grown quantum wells. Particularly, we demonstrate that the phase of spin can be locked to propagate in a quantum well with SU(2) symmetry.
Phase-specific magnetic ordering in BiFeO3−PbTiO3
Authors: Comyn Tim P. , Stevenson Tim , Al-Jawad Maisoon , Turner Stuart L. , Smith Ronald I. , Marshall William G. , Bell Andrew J. , Cywinski Robert
Published: December 2008

The multiferroic 0.7 BiFeO3–0.3 PbTiO3 has been fabricated in both sintered ceramic and powder form using conventional mixed oxide synthesis. Rietveld’s analysis of neutron powder diffraction data has shown that the sintered ceramic and powder are predominantly R3c and P4mm phases, respectively. It is shown explicitly that magnetic ordering does not occur for the P4mm phase at room temperature.
Large cavity quantum cascade lasers with InP interstacks
Authors: Bismuto A. , Gresch T. , Bächle A. , Faist Jérôme
Published: December 2008

Multicore quantum cascade lasers with large cavities show low optical losses, high saturation intensity, and low beam divergence. We present a four active core laser based on InGaAs–AlInAs material system emitting at 10.5 μm. To improve thermal conductance, InP interstacks were used to separate active regions. Selective lateral etching of the active regions was used to reduce optical losses. Peak powers up to 4.6 W, average powers up to 310 mW, and wall-plug efficiencies up to 4.6% were measured at 300 K. A far field with full width at half maximum of 18.7° and 49.8° in the lateral and in the growth direction, respectively, was observed.
Positive ion polymerization in hydrogen diluted silane plasmas
Authors: Nunomura S. , Kondo M.
Published: December 2008

Mass spectra of positive ions (cations) and neutrals have been measured in hydrogen diluted silane plasmas at gas pressures of 0.1–10 Torr. The mass spectrum of ions changes with the pressure, while that of neutrals maintains a similar shape. The dominant ion species varies from a hydrogen ion group at ≲0.5 Torr to a monosilicon hydride ion group at ≈0.5–1 Torr and polysilicon hydride ion groups at ≳1 Torr, which is determined from ionization channels and consecutive ion-molecule reactions. The ion bombardment is suppressed with the pressure, from several tens of eV at ≲1 Torr to a few eV at ≳7 Torr.
Atomic ordering and magnetic properties in the Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy
Authors: Ito W. , Nagasako M. , Umetsu R. Y. , Kainuma R. , Kanomata T. , Ishida K.
Published: December 2008

The effects of chemical order on the phase stability and magnetic properties of the metamagnetic shape memory alloy Ni45Co5Mn36.7In13.3 were investigated. Alloys quenched from the B2 and L21 phase regions were found to transform to the L10 and 6M martensite phases, respectively. For alloys quenched from the B2 region the martensitic transformation starting temperature is about 80 K higher than that for alloys quenched from the L21 region. The Curie temperature of the parent phase and the magnetization of the martensite phase were both lower for the alloy quenched from the B2 region than those for the alloy quenched from L21 region.
Enhanced four-wave mixing by atomic coherence in a Pr3+:Y2SiO5 crystal
Authors: Wang Hai-Hua , Du Dun-Mao , Fan Yun-Fei , Li Ai-Jun , Wang Lei , Wei Xiao-Gang , Kang Zhi-Hui , Jiang Yun , Wu Jin-Hui , Gao Jin-Yue
Published: December 2008

We experimentally demonstrate an enhanced four-wave mixing (FWM) based on atomic coherence in a Pr3+:Y2SiO5 crystal. By employing coherent population return and fractional stimulated Raman adiabatic passage to prepare maximum atomic coherence in the crystal, an efficient FWM signal can be generated. By measuring the generated FWM signal, the time-dependent atomic coherence is monitored. Such an enhanced FWM in solids may have practical applications in nonlinear optics and laser spectroscopy.
Subwavelength imaging of acoustic waves by a canalization mechanism in a two-dimensional phononic crystal
Authors: He Zhaojian , Cai Feiyan , Ding Yiqun , Liu Zhengyou
Published: December 2008

In this letter, the subwavelength imaging of acoustic waves is reported based on a mechanism that the evanescent modes of a source are canalized by the Bloch modes of a two-dimensional phononic crystal that served as the lens. The phononic crystal was designed to have a thickness that meets the condition of Fabry–Pérot resonance in order to enhance wave transmission and hence to improve imaging performance. Numerical simulations demonstrated that for a point acoustic source an image as small as 0.16λ can be formed.
Experimental demonstration of a μ=−1 metamaterial lens for magnetic resonance imaging
Authors: Freire Manuel J. , Marques Ricardo , Jelinek Lukas
Published: December 2008

In this work a μ=−1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radio frequency (rf) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the rf field detected by these surface coils so that the coil sensitivity and spatial localization are substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of rf field in MRI, which paves the way to many other interesting applications.
Growth and magnetic control of twinning structure in thin films of Heusler shape memory compound Ni2MnGa
Authors: Jenkins C. A. , Ramesh R. , Huth M. , Eichhorn T. , Pörsch P. , Elmers H. J. , Jakob G.
Published: December 2008

Twin structure engineering in sputtered films close to the Heusler stoichiometry Ni2MnGa (001) is used to demonstrate temperature and magnetic control of the phase transformation behavior. A custom heating apparatus integrated with a commercial microscope allows the observation of the austenite-martensite transition in epitaxially clamped films. Intermartensitic twin boundaries on cantilevers released from the epitaxial strain by focused ion beam etching are shown to move in response to an applied magnetic field with a strength of 0.6 T. We also report the observation of two coexisting twin morphologies.
Electronic structure of single-walled carbon nanotubes on ultrathin insulating films
Authors: Shin Hyung-Joon , Clair Sylvain , Kim Yousoo , Kawai Maki
Published: December 2008

The electronic structures of single-walled carbon nanotubes on Ag(100) and on ultrathin insulating NaCl(100)/Ag(100) were studied using low-temperature scanning tunneling microscopy. The Fermi level of the nanotubes was shifted toward the conduction band on Ag(100), while it was shifted toward the valence band on NaCl films. We explain this opposite behavior by different basic mechanisms accounting for the Fermi level shifts. On the metal surface, the work function difference between the tube and the substrate determines the direction of the Fermi level shift. In the case of carbon nanotubes on insulating films, the electric field resulting from the dipole moment formed at the interface between the insulating film and the metal plays a decisive role in determining the Fermi level.
How Normal is Travelling Abroad? Differences in Transnational Mobility between Groups of Young Swedes
Authors: Frändberg Lotta
Published: December 2008

Travel across national borders is growing rapidly as a consequence of greater ease, and access to fast means, of transport, but also due to the reorganization of society and the stretching of social relations over large distances. Much recent writing on transnational mobility has argued that long-distance travel is increasingly a normal and sometimes a necessary part of ordinary life for many people in richer countries. This paper investigates differences in the extent of transnational mobility between groups of Swedish youth with different socioeconomic and ethnic backgrounds. The study includes eight groups (162 individuals) of students in the last year of senior secondary school (16–19 years old). Comparisons are based on the respondents' mobility biographies—information about all trips abroad taken during childhood and adolescence. One important finding of the study is the very large difference in transnational mobility—in particular, aeromobility—between the most mobile group and the other groups. Those in the most mobile group attend a privately run school in a central urban location; the majority of students in this group have at least one parent in a managerial position. The study also finds that there is a substantial difference in transnational mobility between youth living in an urban versus a rural environment. Taken together, the results confirm the idea of transnational mobility as a critical differentiating factor. Furthermore, the results presented here do not assign transnational social relations a prominent role in shaping the distribution of mobility between youth belonging to different social groups in Swedish society. Of overwhelming importance in this respect is the extent to which holiday leisure travel is available and prioritized.
Multilevel Governance, Networking Cities, and the Geography of Climate-Change Mitigation: Two Swedish Examples
Authors: Gustavsson Eva , Elander Ingemar , Lundmark Mats
Published: December 2008

What geographical and institutional conditions are important for initiating and sustaining climate-change mitigation at the local level? Taking this question as a point of departure, we analyze local climate mitigation as a case of multilevel network governance. This is illustrated by the case of two Swedish cities, which are both involved in city networking in favour of climate-change mitigation. Different business structures and other local conditions in significant ways influence both the level of ambition and the climate-policy strategies of the two cities. The sheer size and intensity of the networking activities clearly illustrate the fact that cities are increasingly becoming arenas of globalization, rather than passive victims of global forces, thus confirming the call for a multilevel network-governance approach in policy and politics as well as in research.
Converging Agendas? Energy and Climate Change Policies in the UK
Authors: Lovell Heather , Bulkeley Harriet , Owens Susan
Published: December 2008

In the UK climate change and energy have converged on the policy agenda. We discuss the implications for theories of policy change based on well-defined networks located within single, discrete, policy domains. We suggest that such approaches struggle to account for the dynamics of change in conditions of policy convergence. The issue of climate change has opened up and destabilised the UK energy policy sector, but this process has been surprisingly free of conflict, despite radical policy shifts. To date, convergence of the energy and climate change sectors has largely occurred at a discursive level, and we focus our attention on a number of different, but largely complementary, storylines about solutions to climate change. We draw on ideas about sociotechnical regime transitions, first, to explore why the storylines are not in obvious conflict, and, second, to identify small-scale niches where tensions in storylines do emerge as discourse is translated into material reality.
Graphical Illustration and Functional Neuroimaging of Visual Hallucinations during Prolonged Blindfolding: A Comparison to Visual Imagery
Authors: Sireteanu Ruxandra , Oertel Viola , Mohr Harald , Linden David , Singer Wolf
Published: December 2008

Visual hallucinations can occur in healthy subjects during prolonged visual deprivation. We investigated the visual percepts and the associated brain activity in a 37-year-old healthy female subject who developed visual hallucinations during three weeks of blindfolding, and then compared this activity with the cortical activity associated with mental imagery of the same patterns. We acquired fMRI data with a Siemens 3T Magnetom Allegra towards the end of the deprivation period to assess hallucination-related activity, and again after recovery from blindfolding to measure imagery-related activity. Detailed subjective descriptions and graphical illustrations were provided by the subject after blindfolding was completed. The subject reported the occurrence of simple and elementary hallucinations, consisting of flashes and coloured and moving patterns during the period of blindfolding. Neural activity related to hallucinations was found in extrastriate occipital, posterior parietal, and several prefrontal regions. In contrast, mental imagery of the same percepts led to activation in prefrontal, but not in posterior, parietal, and occipital regions. These results suggest that deprivation-induced hallucinations result from increased excitability of extrastriate visual areas, while mentally induced imagery involves active read-out under the volitional control of prefrontal structures. This agrees with the subject's report that visual hallucinations were more vivid than mental imagery.
Simultaneous Color Contrast in 4-Month-Old Infants
Authors: Pereverzeva Maria , Teller Davida Y
Published: December 2008

The present paper addresses the question of simultaneous color contrast in 4-month-old human infants. A temporal modulation paradigm was employed for infant testing. In this paradigm, infants viewed two test disks presented side-by-side: one of unchanging chromaticity (static) and another of the chromaticity varied in time (temporally modulated). The test stimuli were embedded in a surround that was either static or temporally modulated in phase with the modulated test stimulus. The temporally modulated test stimuli were chosen in such a way as to appear static to adults when viewed in the temporally modulated surround. On the basis of the observation that infants prefer to look more at flickering stimuli, the prediction is that, if infants have adult-like simultaneous color contrast, their preference for the temporally modulated stimulus should decrease and their preference for the static stimulus should increase when the surround is also temporally modulated as described. In concordance with this prediction, a significant increase in preference for the temporally static stimuli was observed with the introduction of temporal modulation in the surround. The data are consistent with the conclusion that infants as young as 4 months of age have simultaneous color contrast.
Aneuploid sperm formation in rainbow trout exposed to the environmental estrogen 17α-ethynylestradiol
Authors: Brown Kim H. , Schultz Irvin R. , Cloud J. G. , Nagler James J.
Published: December 2008

Environmental contaminants that mimic native estrogens (i.e., environmental estrogens) are known to significantly impact a wide range of vertebrate species and have been implicated as a source for increasing human male reproductive deficiencies and diseases. Despite the widespread occurrence of environmental estrogens and recognized detrimental effects on male vertebrate reproduction, no specific mechanism has been determined indicating how reduced fertility and/or fecundity is achieved. Previous studies show that male rainbow trout,Oncorhynchus mykiss, exposed to the environmental estrogen 17α-ethynylestradiol (EE2) before gamete formation and fertilization produce progeny with significantly reduced embryonic survival. To determine whether this observed decrease results from sperm chromosome alterations during spermatogenesis, male rainbow trout were exposed to 10 ng of EE2/l for 50 days. After exposure, semen was collected and sperm aneuploidy levels analyzed with two chromosome markers by fluorescentin situhybridization.In vitrofertilizations were also conducted by using control and exposed sperm crossed to eggs from an unexposed female for offspring analysis. Evaluations for nucleolar organizer region number and karyotype were performed on developing embryos to determine whether sperm aneuploidy translated into embryonic aneuploidy. Results conclusively show increased aneuploid sperm formation due to EE2 exposure. Additionally, embryonic cells from propagated progeny of individuals possessing elevated sperm aneuploidy display high levels of embryonic aneuploidy. This study concludes that EE2 exposure in sexually developing male rainbow trout increases levels of aneuploid sperm, providing a mechanism for decreased embryonic survival and ultimately diminished reproductive success in EE2 exposed males.