bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors
Authors: Allen M. W. , Zemlyanov D. Y. , Waterhouse G. I. N. , Metson J. B. , Veal T. D. , McConville C. F. , Durbin S. M.
Published: March 2011

Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.
Reversible electron pumping and negative differential resistance in two-step barrier diode under strong terahertz ac field
Authors: Murillo G. , Schulz P. A. , Arce J. C.
Published: March 2011

A computational study, employing a Floquet-transfer-matrix approach, of the current in a model two-step barrier diode under intense ac fields in the terahertz range is reported. It is demonstrated that the field pumps a net tunnel current through the structure, which can exhibit a negative differential resistance and whose direction can be controlled by the ac-bias amplitude. These behaviors are seen to originate from the inelastic scattering of incoming electrons by absorption or emission of field quanta from a shape resonance present in the field-free structure.
Fast electron accumulation and its mechanism in a harmonic trap under ultrahigh vacuum conditions
Authors: Mohamed T. , Imao H. , Oshima N. , Mohri A. , Yamazaki Y.
Published: March 2011

We present here a fast and efficient electron accumulation in a multiring trap (MRT) in a superconducting solenoid of 5 T. More than 1010 electrons were accumulated within a fraction of a second for an electron beam in the range of 10−7 A. The MRT was installed in a cryogenic bore tube cooled down to ∼10 K. Electron accumulation as a function of various parameters such as the beam intensity, the MRT depth, and the MRT length was studied. We succeeded in extracting a consistent picture of the electron accumulation mechanisms, which consist of interactions of the incoming electron beam with the reflected beam and with the electrons trapped in the MRT.
Noncommutative oscillators from a Hopf algebra twist deformation. A first principles derivation
Authors: Castro P. G. , Chakraborty B. , Kullock R. , Toppan F.
Published: March 2011

Noncommutative oscillators are first-quantized through an abelian Drinfel'd twist deformation of a Hopf algebra and its action on a module. Several important and subtle issues making the quantization possible are solved. The spectrum of the single-particle Hamiltonians is computed. The multiparticle Hamiltonians are fixed, unambiguously, by the Hopf algebra coproduct. The symmetry under particle exchange is guaranteed. In d = 2 dimensions the rotational invariance is preserved, while in d = 3 the so(3) rotational invariance is broken down to an so(2) invariance.
Active black holes: Relevant plasma structures, regimes and processes involving all phase space
Authors: Coppi Bruno
Published: March 2011

The presented theory is motivated by the growing body of experimental information on the characteristics, connected with relevant spectral, time, and space resolutions, of the radiation emission from objects considered as rotating black holes. In the immediate surroundings of these objects, three plasma regions are identified: an innermost Buffer Region, an intermediate Three-regime Region, and a Structured Peripheral Region. In the last region, a Composite Disk Structure made of a sequence of plasma rings corresponding to the formation of closed magnetic surfaces is considered to be present and to allow intermittent accretion flows along the relevant separatrices. The nonlinear “Master Equation” describing composite disk structures is derived and solved in appropriate asymptotic limits. A ring configuration, depending on the state of the plasma at the microscopic level: (i) can be excluded from forming given the strongly nonthermal nature of the electron distribution (in momentum space) within the Three-regime Region allowing the onset of a spiral structure; the observed High Frequency Quasi Periodic Oscillations are associated with these tridimensional structures; (ii) may be allowed to propagate to the outer edge of the Buffer Region where successive rings carrying currents in opposite directions are ejected vertically (in opposite directions) and originate the observed jets; or (iii) penetrates in the Three-regime Region and is dissipated before reaching the outer edge of the Buffer Region. The absence of a coherent composite disk structure guiding accretion in the presence of a significant magnetic field background is suggested to characterize quiescent black holes.
Study on optimal inertial-confinement-fusion hohlraum wall radial density and wall loss
Authors: Zhang Lu , Ding Yongkun , Yang Jiamin , Wu Shunchao , Jiang Shaoen
Published: March 2011

Reducing hohlraum wall loss is one of the most important ways to improve hohlraum coupling efficiency in laser indirect drive inertial-confinement fusion. It is appeared that a high Z metallic foam as hohlraum wall material will reduce wall loss. By adjusting initial hohlraum wall density distribution along radial axes to ρ0(r)=kr, the numerical simulation results show that it can indeed bring best savings of ∼40% general wall loss. We conclude that absorbed energy mainly decreases by restraining rarefactions, and a proper slope k can optimize internal energy loss of low density and increased kinetic loss by subsonic. Also saved energy ratio reduces with source temperature decreasing. This approach would cut the reactor driver that needs quite substantially if experiments demonstrate it.
A portable air jet actuator device for mechanical system identification
Authors: Belden Jesse , Staats Wayne L. , Mazumdar Anirban , Hunter Ian W.
Published: March 2011

System identification of limb mechanics can help diagnose ailments and can aid in the optimization of robotic limb control parameters and designs. An interesting fluid phenomenon—the Coandă effect—is utilized in a portable actuator to provide a stochastic binary force disturbance to a limb system. The design of the actuator is approached with the goal of creating a portable device which could be deployed on human or robotic limbs for in situ mechanical system identification. The viability of the device is demonstrated by identifying the parameters of an underdamped elastic beam system with fixed inertia and stiffness and variable damping. The nonparametric compliance impulse response yielded from the system identification is modeled as a second-order system and the resultant parameters are found to be in excellent agreement with those found using more traditional system identification techniques. The current design could be further miniaturized and developed as a portable, wireless, unrestrained mechanical system identification instrument for less intrusive and more widespread use.
In situ strain relaxation comparison between GaAsBi and GaInAs grown by molecular-beam epitaxy
Authors: France R. , Jiang C.-S. , Ptak A. J.
Published: March 2011

The strain relaxation of GaAsBi is studied in order to determine both the maximum thickness before dislocations form for various misfits and the potential of GaAsBi for usage in the compositionally graded buffer of lattice-mismatched devices. Low-misfit GaAsBi epilayers are grown and compared with GaInAs, a well-studied material currently used in compositional grades. Relaxation behavior and dislocation energetics are compared using in situ wafer curvature. Samples are grown using molecular-beam epitaxy under similar conditions with misfit up to –0.81%. GaAsBi begins to relax at a lower thickness than GaInAs of the same mismatch. This leads to the majority of GaAsBi strain relaxation occurring with less material growth than comparable GaInAs. However, GaAsBi has greater residual strain than GaInAs after 2 μm of growth. These results indicate that GaAsBi requires less elastic energy to form dislocations and more elastic energy to either encourage glide or multiply dislocations than GaInAs. GaAsBi shows less surface roughness than GaInAs for all samples, ruling out roughness as a source of dislocations and hindered glide in these alloys.
Quasispherical fuel compression and fast ignition in a heavy-ion-driven X-target with one-sided illumination
Authors: Henestroza Enrique , Logan B. Grant , Perkins L. John
Published: March 2011

The HYDRA radiation-hydrodynamics code [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is used to explore one-sided axial target illumination with annular and solid-profile uranium ion beams at 60 GeV to compress and ignite deuterium-tritium fuel filling the volume of metal cases with cross sections in the shape of an “X” (X-target). Quasi-three-dimensional, spherical fuel compression of the fuel toward the X-vertex on axis is obtained by controlling the geometry of the case, the timing, power, and radii of three annuli of ion beams for compression, and the hydroeffects of those beams heating the case as well as the fuel. Scaling projections suggest that this target may be capable of assembling large fuel masses resulting in high fusion yields at modest drive energies. Initial two-dimensional calculations have achieved fuel compression ratios of up to 150X solid density, with an areal density ρR of about 1 g/cm2. At these currently modest fuel densities, fast ignition pulses of 3 MJ, 60 GeV, 50 ps, and radius of 300 μm are injected through a hole in the X-case on axis to further heat the fuel to propagating burn conditions. The resulting burn waves are observed to propagate throughout the tamped fuel mass, with fusion yields of about 300 MJ. Tamping is found to be important, but radiation drive to be unimportant, to the fuel compression. Rayleigh–Taylor instability mix is found to have a minor impact on ignition and subsequent fuel burn-up.
High-speed nanometer-resolved imaging vibrometer and velocimeter
Authors: Mahjoubfar Ata , Goda Keisuke , Ayazi Ali , Fard Ali , Kim Sang Hyup , Jalali Bahram
Published: March 2011

Conventional laser vibrometers are incapable of performing multidimensional vibrometry at high speeds because they build on single-point measurements and rely on beam scanning, significantly limiting their utility and precision. Here we introduce a laser vibrometer that performs high-speed multidimensional imaging-based vibration and velocity measurements with nanometer-scale axial resolution without the need for beam scanning. As a proof-of-concept, we demonstrate real-time microscopic imaging of acoustic vibrations with 1 nm axial resolution, 1200 image pixels, and 30 ps dwell time at 36.7 MHz scan rate.
Influence of the substrate temperature on the Curie temperature and charge carrier density of epitaxial Gd-doped EuO films
Authors: Mairoser T. , Schmehl A. , Melville A. , Heeg T. , Zander W. , Schubert J. , Shai D. E. , Monkman E. J. , Shen K. M. , Regier T. Z. , Schlom D. G. , Mannhart J.
Published: March 2011

Rare earth doping is a standard, yet experimentally poorly understood method to increase the Curie temperature (TC) of the ferromagnetic semiconductor EuO. Here, we report on the charge carrier density (n) and the TC of commonly used 4.2 at. % Gd-doped EuO films grown by molecular-beam epitaxy on (110) oriented YAlO3 substrates at various substrate temperatures (Tsub). Increasing Tsub leads to a decrease in n and TC. For high substrate temperatures the Gd-doping is rendered completely inactive: n and TC drop to the values of undoped EuO.
Very long wavelength quantum dot infrared photodetector using a modified dots-in-a-well structure with AlGaAs insertion layers
Authors: Wei Yang , Ma Wenquan , Huang Jianliang , Zhang Yanhua , Huo Yongheng , Cui Kai , Chen Lianghui , Shi Yanli
Published: March 2011

We report a modified dots-in-a-well (DWELL) infrared photodetector by inserting some very thin GaAs or AlGaAs layers into the InAs dots. The photoluminescence (PL) measurements indicate that the modified DWELL structure with the insertion layers (ILs) of GaAs has a larger peak intensity and a narrower PL linewidth than that without the ILs. For the modified DWELL detector with AlGaAs ILs, the peak detection wavelength reaches very long infrared window of 14.1 μm. The peak detectivity D∗ is 1.1×108 cm Hz1/2/W at 77 K under normal incidence infrared irradiation.
Effect of high-pressure oxygen annealing on negative bias illumination stress-induced instability of InGaZnO thin film transistors
Authors: Ji Kwang Hwan , Kim Ji-In , Jung Hong Yoon , Park Se Yeob , Choi Rino , Kim Un Ki , Hwang Cheol Seong , Lee Daeseok , Hwang Hyungsang , Jeong Jae Kyeong
Published: March 2011

Negative-bias illumination stress (NBIS) of amorphous InGaZnO (IGZO) transistors can cause a large negative shift (>7.1 V) in threshold voltage, something frequently attributed to the trapping of photoinduced hole carriers. This work demonstrates that the deterioration of threshold voltage by NBIS can be strongly suppressed by high-pressure annealing under 10 atm O2 ambient. This improvement occurred through a reduction in oxygen vacancy defects in the IGZO film, indicating that a photoinduced transition from VO to VO2+ was responsible for the NBIS-induced instability.
Preparation of ferroelectric field effect transistor based on sustainable strongly correlated (Fe,Zn)3O4 oxide semiconductor and their electrical transport properties
Authors: Takaobushi Junichi , Kanki Teruo , Kawai Tomoji , Tanaka Hidekazu
Published: March 2011

We have constructed a field effect transistor structure composed of the sustainable oxide semiconductor (Fe,Zn)3O4 with high Curie temperature and ferroelectric Pb(Zr,Ti)O3. Electric field control of (Fe2.5Zn0.5)O4 channel resistance was achieved in the heterostructures though modulation of their carrier concentration. The results will lead to the significant development of sustainable oxide semiconductor spintronics devices working at room temperature.
Ultrafast cross saturation dynamics in inhomogeneously broadened InAs/InP quantum dash optical amplifiers
Authors: Capua A. , Eisenstein G. , Reithmaier J. P.
Published: March 2011

We describe multiwavelength pump probe characterization of an inhomogeneously broadened semiconductor nanostructure gain medium. An InAs/InP quantum-dash optical amplifier is perturbed by a 100 fs pulse and the response is measured at wavelengths outside the homogeneously broadened spectral region. Energy dependent carrier cross relaxation as well as capture and escape processes are investigated and quantified.
Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement
Authors: Effenberger Frederic , Thust Kay , Arnold Lukas , Grauer Rainer , Dreher Jürgen
Published: March 2011

The formation of a thin current sheet in a magnetic quasiseparatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-β, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al. [Astron. Astrophys. 444, 961 (2005)]. In extension to that work, we use the technique of adaptive mesh refinement (AMR) to significantly enhance the local spatial resolution of the current sheet during its formation, which enables us to follow the evolution into a later stage. Our simulations are in good agreement with the results of Aulanier et al. up to the calculated time in that work. In a later phase, we observe a basically unarrested collapse of the sheet to length scales that are more than one order of magnitude smaller than those reported earlier. The current density attains correspondingly larger maximum values within the sheet. During this thinning process, which is finally limited by lack of resolution even in the AMR studies, the current sheet moves upward, following a global expansion of the magnetic structure during the quasistatic evolution. The sheet is locally one-dimensional and the plasma flow in its vicinity, when transformed into a comoving frame, qualitatively resembles a stagnation point flow. In conclusion, our simulations support the idea that extremely high current densities are generated in the vicinities of QSLs as a response to external perturbations, with no sign of saturation.
Substrate heating influence on the deposition rate of oxides during pulsed laser deposition in ambient gas
Authors: Amoruso S. , Aruta C. , Bruzzese R. , Wang X. , Scotti di Uccio U.
Published: March 2011

We investigate the effects of ambient pressure and substrate temperature on the deposition rate of oxides grown by pulsed laser deposition in oxygen atmosphere. The deposition rate of LaGaO3 (LGO) and LaAlO3 (LAO) is studied at room temperature by means of a quartz crystal microbalance and at 800 °C by exploiting reflection high energy electron diffraction. We observe a clear dependence of the deposition rate on temperature for an oxygen pressure between 10−2 and 1 mbar. A simple model based on multiple-elastic-scattering processes thoroughly describes the observed dependence of the deposition rate on the pressure/density of the background gas.
Evolution of RESET current and filament morphology in low-power HfO2 unipolar resistive switching memory
Authors: Hou Tuo-Hung , Lin Kuan-Liang , Shieh Jiann , Lin Jun-Hung , Chou Cheng-Tung , Lee Yao-Jen
Published: March 2011

Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/HfO2/Si structure with low RESET current of 50 μA and RESET power of 30 μW. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current.
Schottky-barrier lowering in silicon nanowire field-effect transistors prepared by metal-assisted chemical etching
Authors: Zaremba-Tymieniecki M. , Durrani Z. A. K.
Published: March 2011

We investigate the influence of Schottky barrier lowering in Si nanowire field-effect transistors, using nanowires prepared by metal-assisted chemical etching. The experimental electrical characteristics of a p-channel transistor are modeled using thermionic emission of holes across the reverse-biased source Schottky barrier. This barrier is lowered by the image-force potential, and by the electric field generated by both source-drain and gate voltages. The gate voltage lowers the barrier height directly and in addition, modulates the effect of the source-drain voltage on barrier lowering.
Hillslope runoff and erosion on duplex soils in grazing lands in semi-arid central Queensland. I. Influences of cover, slope, and soil
Authors: Silburn D. M. , Carroll C. , Ciesiolka C. A. A. , deVoil R. C. , Burger P.
Published: March 2011

Many soils in semi-arid grazing lands develop low pasture cover or bare areas (scalds) under heavy grazing and have a low tolerance to soil erosion, due to low total water-holding capacity and concentration of nutrients in the soil surface. Runoff and erosion was measured for 7 years on 12 hillslope plots with cover (pasture plus litter) ranging from 10 to 80%, slopes from 4 to 8%, with and without grazing, with and without tree canopy cover, on a variety of soils. Soils were grouped into those derived from sandstone (SS), mudstone (MS), and eroded mudstone (MSe). One plot with low cover had a grass filter at the outlet.
Runoff was strongly influenced by surface cover and was high with low cover (200–300 mm/year or 30–50% of rainfall). Runoff averaged 35 mm/year or 5.9% of rainfall with >50% cover. All soils fitted the same runoff–cover relationship. The grass filter had no effect on runoff and suspended load, but did reduce bedload. Grass pasture cover and tree litter cover were equally effective in controlling runoff and erosion.
Total, bedload, and suspended load sediment concentrations increased linearly with slope in the range 4–8% for plots with low cover, and decreased exponentially with greater cover. Total and bedload sediment–cover relationships were similar for SS, MS, and MSe. However, plots on MSe had higher suspended sediment losses and thus slightly higher total soil losses. For all soils, erosion resulted in low sediment concentrations due to the hard-set surface soil, but total soil losses were high due to the large volumes of runoff generated.
Concentration–cover relationships were different for bedload and suspended sediment. Consequently, suspended sediment was 20–40% of total soil loss for bare soil, and increased with cover to about 80% with cover >80%. The proportion of suspended sediment for bare soil was similar to the proportion of dispersed silt plus clay in the surface soil. About 90% of suspended sediment was fine-sized (<0.053 mm). Bedload was mainly coarse and fine sands, which were enriched compared with the surface soil.
Grazing in semi-arid pastures should be managed to maintain >50% ground cover to avoid excessive runoff and soil erosion, and degradation of soil productivity, and to maintain good off-site water quality.
Hillslope runoff and erosion on duplex soils in grazing lands in semi-arid central Queensland. II. Simple models for suspended and bedload sediment
Authors: Silburn D. M.
Published: March 2011

The use of simple models of soil erosion which represent the main effects of management in grazing lands in northern Australia is limited by a lack of measured parameter values. In particular, parameters are needed for erosion models (sediment concentration v. cover equations) used in daily soil-water balance models. For this research, we specifically avoided equations that use rainfall and runoff rates (e.g. peak flow), as current daily models are limited in their ability to estimate these rates. The resulting models will therefore give poor estimates of soil losses for individual events, but should give good estimates of long-term average erosion and management influences.
Runoff and erosion data were available for 7 years on 12 hillslope plots with cover of 10–80%, with and without grazing, with and without tree canopy cover, on a variety of soils according to various soil classification systems. Soils were grouped into those derived from sandstone (SS), mudstone (MS), and eroded mudstone (MSe). These data were used to determine two parameters, i.e. (i) efficiency of entrainment for bare soil and (ii) a cover factor, for simple models of bedload and suspended sediment concentrations. Methods used to fit parameters affected the results; optimising to obtain the minimum sum of squares of errors in soil losses gave better results than fitting an exponential equation to sediment concentration–cover data.
The use of a linear slope factor in the sediment concentration models was confirmed with data from plots with slopes 4–8%. Parameters for the bedload sediment concentration model were the same for SS, MS, and MSe soils. Parameters for the suspended sediment concentration model were the same for SS and MS soils, but the MSe soil had a greater efficiency of entrainment for bare soil (about double). The sediment concentration–cover relationships and fitted cover factors were different for suspended and bedload sediment. Thus, the resulting modelled proportion of sediment as suspended load changed with cover, from ~0.3 for bare soil to 0.9 at 80% cover, mimicking the measured data. The cover factor was lower than published values for cultivated soils, indicating less reduction in sediment concentration with greater cover. A compilation of parameter values for the sediment concentration model from published and unpublished sources in grazing and cropping lands is provided.
Influence of soil faunal communities on nitrogen dynamics in legume-based mesocosms
Authors: Schon N. L. , Mackay A. D. , Hedley M. J. , Minor M. A.
Published: March 2011

Soil invertebrates play an important part in nutrient supply. It has been suggested that invertebrates have the greatest influence on nitrogen (N) availability in soils of low N fertility, and therefore invertebrates may be less important in pastoral systems with high N inputs. The influence of invertebrates on N cycling, and the fate of 15N-labelled plant litter, in a low- or high-N environment and in a soil with low or high bulk density were explored by the introduction of different elements of the invertebrate community in constructed soil ryegrass–white clover mesocosms. At high bulk density and low N, the N made available by invertebrates resulted in higher plant growth, without any increases in N losses to the environment. At high N, where pasture growth was not limited by N, the N made available by invertebrates increased both herbage N% and the amount of N in leachate. More of the 15N-labelled plant litter decomposed in high-N than low-N mesocosms. Invertebrates increased the plant uptake of surface-applied 15N plant litter. The influence of invertebrates was dependent on bulk density, suggesting that invertebrates in compacted soils improved soil structure and N availability. This mesocosm study highlights the important role of invertebrates in N supply across a range of soil conditions.
Impact of successive sugarcane harvests and trash management practices on soil microbiological properties
Authors: Pupin Breno , Nahas Ely
Published: March 2011

Sugarcane culture is replanted after five–eight successive harvests and intensely fertilised and mechanised. The influence on bacteria (total, nitrifying, denitrifying), fungi, microbial biomass-C, and dynamic processes (respiratory activity, N mineralisation, potential nitrification, P-solubilising activity) and enzymatic activities (dehydrogenase, urease, phosphatase) was studied for six successive harvests of the crop. The straw of the second and third harvest was burned. Soil microbial counts and activities were reduced after successive harvests. Fungi counts, N mineralisation, potential nitrification, and the P-solubilising, urease, and phosphatase activities decreased gradually from the first harvest to the third, increased again after the fourth, and then decreased again. Total, nitrifying, and denitrifying bacteria and fungi counts decreased, on average, 55, 22, 17, and 77%, respectively, in the sixth harvest in relation to the first. Reductions also occurred in microbial biomass-C (43%), respiratory activity (39%), N mineralisation (35%), potential nitrification (40%), and P-solubilising activity (35%). Reductions were observed in dehydrogenase (58%) and urease (36%) activities, but not in phosphatase activity. Successive sugarcane harvests may significantly influence microbial populations and activities, with harmful consequences to the C, N, and P cycles, and may decrease crop productivity.
Large shifts in pK
a
values of lysine residues buried inside a protein
Authors: Isom Daniel G. , Castañeda Carlos A. , Cannon Brian R. , García-Moreno E. Bertrand
Published: March 2011

Internal ionizable groups in proteins are relatively rare but they are essential for catalysis and energy transduction. To examine molecular determinants of their unusual and functionally important properties, we engineered 25 variants of staphylococcal nuclease with lysine residues at internal positions. Nineteen of the Lys residues have depressed pK
a
values, some as low as 5.3, and 20 titrate without triggering any detectable conformational reorganization. Apparently, simply by being buried in the protein interior, these Lys residues acquired pK
a
values comparable to those of naturally occurring internal ionizable groups involved in catalysis and biological H
+
transport. The pK
a
values of some of the internal Lys residues were affected by interactions with surface carboxylic groups. The apparent polarizability reported by the pK
a
values varied significantly from location to location inside the protein. These data will enable an unprecedented examination of the positional dependence of the dielectric response of a protein. This study also shows that the ability of proteins to withstand the presence of charges in their hydrophobic interior is a fundamental property inherent to all stable proteins, not a specialized adaptation unique to proteins that evolved to depend on internal charges for function.
Understanding dopamine and reinforcement learning: The dopamine reward prediction error hypothesis
Authors: Glimcher Paul W.
Published: March 2011

A number of recent advances have been achieved in the study of midbrain dopaminergic neurons. Understanding these advances and how they relate to one another requires a deep understanding of the computational models that serve as an explanatory framework and guide ongoing experimental inquiry. This intertwining of theory and experiment now suggests very clearly that the phasic activity of the midbrain dopamine neurons provides a global mechanism for synaptic modification. These synaptic modifications, in turn, provide the mechanistic underpinning for a specific class of reinforcement learning mechanisms that now seem to underlie much of human and animal behavior. This review describes both the critical empirical findings that are at the root of this conclusion and the fantastic theoretical advances from which this conclusion is drawn.
Surface description and defect detection by wavelet analysis
Authors: Rosenboom Lars , Kreis Thomas , Jüptner Werner
Published: March 2011

Wavelet analysis is a method to describe single- or multi-dimensional signals in multiple scales. Optically measured two-dimensional height data describing engineering surfaces are effectively represented by wavelet transforms enabling a reliable description of even complicated formed surfaces by a drastically reduced number of coefficients as well as the detection of component defects of different types. Reconstruction with only 0.1% of all wavelet coefficients of 4-4-pseudo-coiflets leads to a variance of the difference image between original and reconstructed surface of less than 0.07 of the variance of the original surface. Keeping the coefficients with highest values gives an up to four times better result than keeping the coefficients belonging to the lowest frequencies. Defects are effectively detected with the help of Burt–Adelson and Daubechies wavelets. Local defects in the range of 8 nm can be made visible. Lacquer pits are localized in the higher resolution stages of 4-4-pseudo-coiflet-transforms.
Spectral response measurement of double-junction thin-film photovoltaic devices: the impact of shunt resistance and bias voltage
Authors: Pravettoni Mauro , Galleano Roberto , Virtuani Alessandro , Müllejans Harald , Dunlop Ewan D
Published: March 2011

Multijunction photovoltaic (PV) thin-film modules are becoming more and more important on the market, due to their low cost and improved module efficiency now well above 10%. The spectral response (SR) measurement of multijunction thin-film cells presents additional challenges with respect to the SR measurement procedure for single-junction devices. Several works have appeared in the last 15 years in the PV literature, describing certain measurement artefacts that typically appear when measuring the SR of multijunction cells without applying an appropriate voltage bias to the entire cell. In this paper, the authors revise the theoretical description of SR measurements on multijunction devices, show how to detect the possible origin of measurement artefacts from the dark SR and show why bias voltage sometimes is not enough to avoid such artefacts or why it is not even necessary. An experimental confirmation of the theoretical approach is finally given.
Monotonicity and asymptotics of zeros of Laguerre-Sobolev-type orthogonal polynomials of higher order derivatives
Authors: Marcellán Francisco , Rafaeli Fernando
Published: March 2011

In this paper we analyze the location of the zeros of polynomials orthogonal with respect to the inner product
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Holomorphic automorphisms of Danielewski surfaces I — density of the group of overshears
Authors: Kutzschebauch Frank , Lind Andreas
Published: March 2011

We define the notion of shears and overshears on a Danielewski surface. We show that the group generated by shears and overshears is dense (in the compact open topology) in the path-connected component of the identity of the holomorphic automorphism group.
N-cadherin–mediated cell adhesion restricts cell proliferation in the dorsal neural tube
Authors: Chalasani Kavita , Brewster Rachel M.
Published: March 2011

Neural progenitors are organized as a pseudostratified epithelium held together by adherens junctions (AJs), multiprotein complexes composed of cadherins and α- and β-catenin. Catenins are known to control neural progenitor division; however, it is not known whether they function in this capacity as cadherin binding partners, as there is little evidence that cadherins themselves regulate neural proliferation. We show here that zebrafish N-cadherin (N-cad) restricts cell proliferation in the dorsal region of the neural tube by regulating cell-cycle length. We further reveal that N-cad couples cell-cycle exit and differentiation, as a fraction of neurons are mitotic in N-cad mutants. Enhanced proliferation in N-cad mutants is mediated by ligand-independent activation of Hedgehog (Hh) signaling, possibly caused by defective ciliogenesis. Furthermore, depletion of Hh signaling results in the loss of junctional markers. We therefore propose that N-cad restricts the response of dorsal neural progenitors to Hh and that Hh signaling limits the range of its own activity by promoting AJ assembly. Taken together, these observations emphasize a key role for N-cad–mediated adhesion in controlling neural progenitor proliferation. In addition, these findings are the first to demonstrate a requirement for cadherins in synchronizing cell-cycle exit and differentiation and a reciprocal interaction between AJs and Hh signaling.
Mes1 controls the meiosis I to meiosis II transition by distinctly regulating the anaphase-promoting complex/cyclosome coactivators Fzr1/Mfr1 and Slp1 in fission yeast
Authors: Kimata Yuu , Kitamura Kenji , Fenner Nicola , Yamano Hiroyuki
Published: March 2011

Meiosis is a specialized form of cell division generating haploid gametes and is dependent upon protein ubiquitylation by the anaphase-promoting complex/cyclosome (APC/C). Accurate control of the APC/C during meiosis is important in all eukaryotic cells and is in part regulated by the association of coactivators and inhibitors. We previously showed that the fission yeast meiosis-specific protein Mes1 binds to a coactivator and inhibits APC/C; however, regulation of the Mes1-mediated APC/C inhibition remains elusive. Here we show how Mes1 distinctively regulates different forms of the APC/C. We study all the coactivators present in the yeast genome and find that only Slp1/Cdc20 is essential for meiosis I progression. However, Fzr1/Mfr1 is a critical target for Mes1 inhibition because fzr1Δ completely rescues the defect on the meiosis II entry in mes1Δ cells. Furthermore, cell-free studies suggest that Mes1 behaves as a pseudosubstrate for Fzr1/Mfr1 but works as a competitive substrate for Slp1. Intriguingly, mutations in the D-box or KEN-box of Mes1 increase its recognition as a substrate by Fzr1, but not by Slp1. Thus Mes1 interacts with two coactivators in a different way to control the activity of the APC/C required for the meiosis I/meiosis II transition.
Morphological and Molecular Characterization of Globodera Populations from Oregon and Idaho
Authors: Skantar A. M. , Handoo Z. A. , Zasada I. A. , Ingham R. E. , Carta L. K. , Chitwood D. J.
Published: March 2011

An unusual population of cyst nematode was found in soils collected from a Powell Butte, OR field with a cropping history including potato, wheat, other crops, and significant weed presence. These nematodes could not be placed with certainty into any known species and exhibited some unique morphological features in some specimens. Compared with Globodera pallida, the cyst body length was slightly longer and the second-stage juvenile stylet length was slightly shorter. In some individuals, the J2 stylet knob height was greater and the tail annules were more prominent than in G. pallida, and the tail abruptly narrowed, with a slight constriction near the posterior third of the hyaline terminus. Compared with G. rostochiensis, the hyaline tail terminus had a larger number of refractive bodies, and cysts of this population had a smaller Granek's ratio and fewer cuticular ridges between the anus and vulva. In some individuals, the tail termini of second-stage juveniles were more bluntly pointed, and the stylet knobs were more anteriorly directed with greater height. Unlike G. tabacum, the cyst wall often lacked a network-like pattern and, in some individuals, the juvenile tail terminus distinctly narrowed after a constriction. Molecularly, the population was distinct from G. pallida, G. rostochiensis, and G. tabacum. Multiplex polymerase chain reaction of the internal transcribed spacer (ITS) rDNA region gave results similar to G. tabacum; however, ITS restriction fragment length polymorphism patterns were observed to have individual bands in common with G. rostochiensis and G. pallida. Phylogenetic analysis based on ITS1 and -2 rDNA sequences showed greatest similarity to populations from Argentina and Chile; together, they form a moderately supported clade, distinct from G. rostochiensis, G. tabacum, G. “mexicana,” European type G. pallida, and several G. pallida populations from South America.
Postharvest Dark Skin Spots in Potato Tubers Are an Oversuberization Response to Rhizoctonia solani Infection
Authors: Buskila Yossi , Tsror (Lahkim) Leah , Sharon Michal , Teper-Bamnolker Paula , Holczer-Erlich Orly , Warshavsky Shimon , Ginzberg Idit , Burdman Saul , Eshel Dani
Published: March 2011

Israeli farmers export 250,000 tons of potato tubers annually, ≈40,000 tons of which are harvested early, before skin set. In recent years, there has been an increase in the occurrence of dark skin spots on early-harvested potato tubers (‘Nicola’) packed in large bags containing peat to retain moisture. The irregular necrotic spots form during storage and overseas transport. Characterization of the conditions required for symptom development indicated that bag temperature after packing is 11 to 13°C and it reaches the target temperature (8°C) only 25 days postharvest. This slow decrease in temperature may promote the establishment of pathogen infection. Isolates from typical lesions were identified as Rhizoctonia spp., and Koch's postulates were completed with 25 isolates by artificial inoculation performed at 13 to 14°C. Phylogenetic analysis, using the internal transcribed spacer sequences (ITS1 and ITS2) of rDNA genes, assigned three isolates to anastomosis group 3 of Rhizoctonia solani. Inoculation of wounded tubers with mycelium of these R. solani isolates resulted in an oversuberization response in the infected area. With isolate Rh17 of R. solani, expression of the suberin biosynthesis-related genes StKCS6 and CYP86A33 increased 6.8- and 3.4-fold, respectively, 24 h postinoculation, followed by a 2.9-fold increase in POP_A, a gene associated with wound-induced suberization, expression 48 h postinoculation, compared with the noninoculated tubers. We suggest that postharvest dark spot disease is an oversuberization response to R. solani of AG-3 infection that occurs prior to tuber skin set.
β2-Adrenergic Receptor Genotype and Other Variables that Contribute to Labor Pain and Progress
Authors: Reitman Elena , Conell-Price Jessamyn , Evansmith Jennifer , Olson Luke , Drosinos Sofia , Jasper Nancy , Randolph Paula , Smiley Richard M. , Shafer Steven , Flood Pamela
Published: March 2011

Background

β2-Adrenergic receptor (β2AR) activity influences labor. Its genotype affects the incidence of preterm delivery. We determined the effect of β2AR genotype on term labor progress and maternal pain.

Methods

We prospectively enrolled 150 nulliparous parturients in the third trimester and obtained sensory thresholds, demographic information, and DNA. Cervical dilation, pain scores, and labor management data were extracted with associated times. The association of genetic and demographic factors with labor was tested using mixed effects models.

Results

Parturients who express Gln at the 27 position of the β2AR had slower labor (P < 0.03). They progressed from 1-10 cm dilation in approximately 21 h compared with 14 h among other patients. Asian ethnicity, previously associated with slower labor, is highly associated with this polymorphism (P < 0.0001). Heavier and black patients had slower latent labor (P < 0.01, 0.01). Neuraxial analgesia was associated with slower labor progress (P < 0.0001). It could take up to 36 h for parturients who were black and/or more than median weight (165 lb) to transition from 1 cm cervical dilation to active labor. However, after this active phase began, labor rates among these patients were similar to that of other parturients.

Conclusions

We detected a strong association between β2AR genotype and slower labor. Asian ethnicity may be a proxy for β2AR genotype. Black women and those of higher than average weight have slower latent labor. These results confirm many of the associations found when this mathematical model was applied to a large retrospective cohort, further validating this approach to description and analysis of labor progress.
Continuous Femoral Nerve Blocks
Authors: Charous Matthew T. , Madison Sarah J. , Suresh Preetham J. , Sandhu NavParkash S. , Loland Vanessa J. , Mariano Edward R. , Donohue Michael C. , Dutton Pascual H. , Ferguson Eliza J. , Ilfeld Brian M.
Published: March 2011

Background

Whether the method of local anesthetic administration for continuous femoral nerve blocks--basal infusion versus repeated hourly bolus doses--influences block effects remains unknown.

Methods

Bilateral femoral perineural catheters were inserted in volunteers (n = 11). Ropivacaine 0.1% was concurrently administered through both catheters: a 6-h continuous 5 ml/h basal infusion on one side and 6 hourly bolus doses on the contralateral side. The primary endpoint was the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle at hour 6. Secondary endpoints included quadriceps MVIC at other time points, hip adductor MVIC, and cutaneous sensation 2 cm medial to the distal quadriceps tendon in the 22 h after initiation of local anesthetic administration.

Results

Quadriceps MVIC for limbs receiving 0.1% ropivacaine as a basal infusion declined by a mean (SD) of 84% (19) compared with 83% (24) for those receiving 0.1% ropivacaine as repeated bolus doses between baseline and hour 6 (paired t test P = 0.91). Intrasubject comparisons (left vs. right) also reflected a lack of difference: the mean basal-bolus difference in quadriceps MVIC at hour 6 was -1.1% (95% CI -22.0-19.8%). The similarity did not reach the a priori threshold for concluding equivalence, which was the 95% CI decreasing within ± 20%. There were similar minimal differences in the secondary endpoints during local anesthetic administration.

Conclusions

This study did not find evidence to support the hypothesis that varying the method of local anesthetic administration--basal infusion versus repeated bolus doses--influences continuous femoral nerve block effects to a clinically significant degree.
Shooting up: the interface of microbial infections and drug abuse
Authors: Kaushik Karishma S. , Kapila Ketoki , Praharaj A. K.
Published: March 2011

Illicit drug control has been on the global agenda for more than a century. Infections have long been recognized as one of the most serious complications of drug abuse. Drug users are susceptible to pulmonary, endovascular, skin and soft tissue, bone and joint, and sexually transmitted infections caused by a wide range of bacterial, viral, fungal and protozoal pathogens. In addition, injection drug users are at increased risk for parenterally acquired infections such as human immunodeficiency virus, hepatitis B virus, hepatitis C virus, tetanus and malaria. Factors related to drug use, such as unsterile injection practices, contaminated drug paraphernalia and drug adulterants, increase the exposure to microbial pathogens. Illicit drugs also affect several components of the complex immune system and thus modulate host immunity. In addition, lifestyle practices such as multiple sexual partners, overcrowded housing arrangements and malnutrition serve as co-factors in increasing the risk of infection. In this review we present an overview of the unique aspects of microbial pathogenesis, immune modulation and common infections associated with drug use. We have restricted the definition of drug abuse to the use of illegal drugs (such as opiates, marijuana, cocaine, heroin and amphetamines), not including alcohol and nicotine.
Recent advances in diagnosis, molecular pathology and therapy of chronic myelomonocytic leukaemia
Authors: Bacher Ulrike , Haferlach Torsten , Schnittger Susanne , Kreipe Hans , Kröger Nicolaus
Published: March 2011

The clinical, morphological, and genetic heterogeneity of chronic myelomonocytic leukaemia (CMML), has made it difficult to clearly assign this entity to a distinct haematological category. In 2001, the World Health Organization transferred CMML to a new category of mixed myeloproliferative/myelodysplastic disorders, which was maintained in the last revision in 2008. Considering the rare occurrence of CMML, most pharmacotherapeutic and transplant studies combined CMML with myelodysplastic syndrome cases, but some clinical trials specifically investigated the use of demethylating agents in CMML and demonstrated stabilization of the haematological situation or even complete remission in subsets of patients. Information on the significance of other drugs is very limited. Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only curative option for patients with CMML. Molecular studies revealed various novel genetic alterations in CMML – notably of the JAK2, TET2, CBL, IDH, or RUNX1 and RAS genes. This review summarizes the current status of pharmacotherapy and transplantation in CMML and outlines recent results of molecular research for diagnosis of this heterogeneous entity.