bluuebunny/crossref_metadata_2025 huggingface dataset:
A mathematical theory of stochastic microlensing. I. Random time delay functions and lensing maps
Authors: Petters A. O. , Rider B. , Teguia A. M.
Published: July 2009

Stochastic microlensing is a central tool in probing dark matter on galactic scales. From first principles, we initiate the development of a mathematical theory of stochastic microlensing. Beginning with the random time delay function and associated lensing map, we determine exact expressions for the mean and variance of these transformations. In addition, we derive the probability density function (pdf) of a random point-mass potential, which form the constituent of a stochastic microlens potential. We characterize the exact pdf of a normalized random time delay function at the origin, showing that it is a shifted gamma distribution, which also holds at leading order in the limit of a large number of point masses if the normalized time delay function was at a general point of the lens plane. For the large number of point-mass limit, we also prove that the asymptotic pdf of the random lensing map under a specified scaling converges to a bivariate normal distribution. We show analytically that the pdf of the random scaled lensing map at leading order depends on the magnitude of the scaled bending angle due purely to point masses as well as demonstrate explicitly how this radial symmetry is broken at the next order. Interestingly, we found at leading order a formula linking the expectation and variance of the normalized random time delay function to the first Betti number of its domain. We also determine an asymptotic pdf for the random bending angle vector and find an integral expression for the probability of a lens plane point being near a fixed point. Lastly, we show explicitly how the results are affected by location in the lens plane. The results of this paper are relevant to the theory of random fields and provide a platform for further generalizations as well as analytical limits for checking astrophysical studies of stochastic microlensing.
Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl
Authors: Alligood Bridget W. , FitzPatrick Benjamin L. , Glassman Emily Jane , Butler Laurie J. , Lau Kai-Chung
Published: July 2009

The dissociation dynamics of methylsulfonyl radicals generated from the photodissociation of CH3SO2Cl at 193 nm is investigated by measuring product velocities in a crossed laser-molecular beam scattering apparatus. The data evidence three primary photodissociation channels of the precursor: S–Cl fission to produce Cl atoms and ground electronic state CH3SO2 radicals, S–Cl fission to produce Cl atoms and electronically excited CH3SO2 radicals, and S–CH3 fission. Some of the vibrationally excited CH3SO2 radicals undergo subsequent dissociation to CH3+SO2, as do all of the electronically excited radicals. The velocities of the SO2 products show that the vibrationally excited ground state CH3SO2 radicals dissociate via a loose transition state having a small exit barrier beyond the endoergicity. Hence, a statistical recoil kinetic energy distribution should and does fit the distribution of velocities imparted to these SO2 products. The electronically excited CH3SO2 radicals also dissociate to CH3+SO2, but with a larger average release to relative kinetic energy. Interestingly, when using 200 eV electron bombardment detection, the ground electronic state CH3SO2 radicals having too little internal energy to dissociate are not observed at the parent CH3SO2+ ion, but only at the CH3+ daughter ion. They are distinguished by virtue of the velocity imparted in the original photolytic step; the detected velocities of the stable radicals are consistent with the calculated barrier of 14.6 kcal/mol for the dissociation of CH3SO2 to CH3+SO2. We present CCSD(T) calculations of the adiabatic excitation energy to the lowest excited state of CH3SO2 radicals, the 1 A2″ state, as well as the vertical energy from the equilibrium geometry of that excited state to the 2 A2″ state, to aid in the experimental assignment.
Energetic neutrals in the cathode sheath of argon direct-current discharges
Authors: Ito Tsuyohito , Cappelli Mark A.
Published: July 2009

We recently reported on the direct measurements of the energy distribution of energetic neutrals incident onto the cathode of an argon dc glow discharge [T. Ito and M. A. Cappelli, Appl. Phys. Lett. 90, 101503 (2007)]. In this paper, we provide a more extensive report of the experimental data, as well as direct comparisons to Monte Carlo simulations in which neutral-neutral and ion-neutral collision processes are modeled with differential scattering cross sections. The experimental results, which are limited to relatively small forward angle sampling in our present configuration, are found to be in excellent agreement with Monte Carlo simulations. The simulations reveal that high energy neutrals are striking the cathode with a wide range of angles, while ions are more anisotropic. Therefore, it is difficult to predict the neutral energy distribution with commonly used simple analytical models that do not consider scattering of neutrals within the sheath. We propose the use of an extended analytical model in this paper, which seems to provide reasonable energy distributions over the range of discharge voltage studied.
Nonmetallic electronegativity equalization and point-dipole interaction model including exchange interactions for molecular dipole moments and polarizabilities
Authors: Smalø Hans S. , Åstrand Per-Olof , Jensen Lasse
Published: July 2009

The electronegativity equalization model (EEM) has been combined with a point-dipole interaction model to obtain a molecular mechanics model consisting of atomic charges, atomic dipole moments, and two-atom relay tensors to describe molecular dipole moments and molecular dipole-dipole polarizabilities. The EEM has been phrased as an atom-atom charge-transfer model allowing for a modification of the charge-transfer terms to avoid that the polarizability approaches infinity for two particles at infinite distance and for long chains. In the present work, these shortcomings have been resolved by adding an energy term for transporting charges through individual atoms. A Gaussian distribution is adopted for the atomic charge distributions, resulting in a damping of the electrostatic interactions at short distances. Assuming that an interatomic exchange term may be described as the overlap between two electronic charge distributions, the EEM has also been extended by a short-range exchange term. The result is a molecular mechanics model where the difference of charge transfer in insulating and metallic systems is modeled regarding the difference in bond length between different types of system. For example, the model is capable of modeling charge transfer in both alkanes and alkenes with alternating double bonds with the same set of carbon parameters only relying on the difference in bond length between carbon σ- and π-bonds. Analytical results have been obtained for the polarizability of a long linear chain. These results show that the model is capable of describing the polarizability scaling both linearly and nonlinearly with the size of the system. Similarly, a linear chain with an end atom with a high electronegativity has been analyzed analytically. The dipole moment of this model system can either be independent of the length or increase linearly with the length of the chain. In addition, the model has been parametrized for alkane and alkene chains with data from density functional theory calculations, where the polarizability behaves differently with the chain length. For the molecular dipole moment, the same two systems have been studied with an aldehyde end group. Both the molecular polarizability and the dipole moment are well described as a function of the chain length for both alkane and alkene chains demonstrating the power of the presented model.
Beamline I11 at Diamond: A new instrument for high resolution powder diffraction
Authors: Thompson S. P. , Parker J. E. , Potter J. , Hill T. P. , Birt A. , Cobb T. M. , Yuan F. , Tang C. C.
Published: July 2009

The performance characteristics of a new synchrotron x-ray powder diffraction beamline (I11) at the Diamond Light Source are presented. Using an in-vacuum undulator for photon production and deploying simple x-ray optics centered around a double-crystal monochromator and a pair of harmonic rejection mirrors, a high brightness and low bandpass x-ray beam is delivered at the sample. To provide fast data collection, 45 Si(111) analyzing crystals and detectors are installed onto a large and high precision diffractometer. High resolution powder diffraction data from standard reference materials of Si, α-quartz, and LaB6 are used to characterize instrumental performance.
Carrier localization in GaBiAs probed by photomodulated transmittance and photoluminescence
Authors: Kudrawiec R. , Syperek M. , Poloczek P. , Misiewicz J. , Mari R. H. , Shafi M. , Henini M. , Gobato Y. Galvão , Novikov S. V. , Ibáñez J. , Schmidbauer M. , Molina S. I.
Published: July 2009

The carrier localization phenomenon has been investigated for GaBiAs by photomodulated transmittance (PT) and photoluminescence (PL). In the case of PT measurements, a decrease in the energy-gap related PT signal has been clearly observed below 180 K. In PL spectra a broad emission band very sensitive to the excitation power has been found. In comparison to the energy-gap related transition, this band is shifted to red. The recombination time for this band at low temperature decreases from 0.7 to 0.35 ns with the increase in the emission energy. All the findings are clear evidences for strong carrier localization in this alloy.
Photoluminescence and electrical transport characteristics of ZnO nanorods grown by vapor-solid technique
Authors: Mandal S. , Sambasivarao K. , Dhar A. , Ray S. K.
Published: July 2009

Hexagonal shaped radial and quasialigned arrays of ZnO nanorods with diameter of about 40–60 nm have been deposited on p-Si (100) substrates by vapor-solid method using Zn as the source material. x-ray diffraction, field emission scanning electron microscopy, temperature dependent-photoluminescence, and impedance spectroscopy have been used to characterize the structural, optical and electrical transport properties of the grown nanostructures. At room temperature, a strong free excitonic emission peak at 3.311 eV with very weak defect emissions is observed. At low temperatures, near-band-edge steady-state photoluminescence spectra of ZnO nanorods are dominated by neutral-donor-bound-exciton (D0X) transitions with corresponding transverse and longitudinal optical phonon replicas. The impedance spectra as a function of bias voltage and temperature have been studied in detail. The differences in characteristics of p-Si/ZnO/Al and Al/ZnO/Al devices are discussed by using one and two RC equivalent circuits. A comparative study of the impedance spectra for bulk ZnO and ZnO nanostructures is presented. The activation energy of ZnO nanorods is found to be 0.08 eV, which is slightly greater than the reported bulk value.
A molecular beam epitaxy facility for in situ neutron scattering
Authors: Dura J. A. , LaRock J.
Published: July 2009

A molecular beam epitaxy (MBE) facility has been built to enable in situ neutron scattering measurements during growth of epitaxial layers. While retaining the full capabilities of a research MBE chamber, this facility has been optimized for polarized neutron reflectometry measurements. Optimization includes a compact lightweight portable design, a neutron window, controllable magnetic field, deposition across a large 76 mm diameter sample with exceptional flux uniformity, and sample temperatures continuously controllable from 38 to 1375 K. A load lock chamber allows for sample insertion, storage of up to 4 samples, and docking with other facilities. The design and performance of this chamber are described here.
Quantum chemical study and experimental observation of a new band system of C2, e Π3g−c Σ3u+
Authors: Nakajima Masakazu , Joester Jenna A. , Page Nathan I. , Reilly Neil J. , Bacskay George B. , Schmidt Timothy W. , Kable Scott H.
Published: July 2009

A new band system of C2, e Π3g−c Σ3u+ was studied by ab initio quantum chemical and experimental methods. The calculations were carried out at the multireference configuration interaction level of theory with Davidson’s correction using aug-cc-pV6Z basis set and include core and core-valence correlation as well as relativistic corrections computed with aug-cc-pCVQZ and cc-pVQZ bases, respectively. The vibrational energies and rotational constants of the upper e Π3g state were calculated from the computed ab initio potential energy curve. The ab initio results indicate that the electronic transition moment of the e Π3g−c Σ3u+ system is approximately one-half that of the Fox–Herzberg e Π3g−a Π3u system. Franck–Condon factors were calculated for both systems and used to guide experiments aimed at discovering the e Π3g−c Σ3u+ system. The e Π3g(v′=4)−c Σ3u+(v″=3) band of jet-cooled C2 was successfully observed by laser-induced fluorescence spectroscopy by monitoring the ensuing e Π3g−a Π3u emission.
Momentum correction techniques for neoclassical transport in stellarators
Authors: Maaßberg H. , Beidler C. D. , Turkin Y.
Published: July 2009

In the traditional neoclassical ordering for stellarators, monoenergetic transport coefficients are evaluated using the simplified Lorentz form of the pitch-angle collision operator which violates momentum conservation. In this paper, the parallel momentum balance with radial parallel momentum transport and viscosity terms is analyzed, in particular, with respect to the radial electric field. Next, the impact of momentum conservation in the stellarator long-mean-free-path regime is estimated for the radial transport and the parallel electric conductivity. Two different momentum correction techniques are described based on monoenergetic transport coefficients calculated by the DKES code [W. I. van Rij and S. P. Hirshman, Phys. Fluids B 1, 563 (1989)]. The benchmarking of the parallel electric conductivity and of the bootstrap current is presented for a tokamak as well as for two W7-X stellarator configurations [G. Grieger et al., Phys. Fluids B 4, 2081 (1992)]. Finally, the impact of the momentum correction on the expected total bootstrap current is briefly analyzed for two W7-X scenarios.
Statistical interpretation of “femtomolar” detection
Authors: Go Jonghyun , Alam Muhammad A.
Published: July 2009

We calculate the statistics of diffusion-limited arrival-time distribution by a Monte Carlo method to suggest a simple statistical resolution of the enduring puzzle of nanobiosensors: a persistent gap between reports of analyte detection at approximately femtomolar concentration and theory suggesting the impossibility of approximately subpicomolar detection at the corresponding incubation time. The incubation time used in the theory is actually the mean incubation time, while experimental conditions suggest that device stability limited the minimum incubation time. The difference in incubation times—both described by characteristic power laws—provides an intuitive explanation of different detection limits anticipated by theory and experiments.
Formation of polymer brushes inside cylindrical pores: A computer simulation study
Authors: Koutsioubas Alexandros G. , Spiliopoulos Nikolaos , Anastassopoulos Dimitris L. , Vradis Alexandros A. , Toprakcioglu Chris
Published: July 2009

The formation process of polymer brushes, formed by the adsorption of flexible end-functionalized chains from dilute solutions on the inner surface of cylindrical pores is studied by bond fluctuation Monte Carlo simulations. Various properties as the grafting density, monomer, and free-end distribution are monitored as a function of pore diameter D and chain length N. Two different modes of end-segment attachment on the inner pore surface are considered: (a) pure-irreversible “hard” grafting and (b) irreversible “soft” grafting where grafted-ends can move freely on the pore surface but cannot detach from it. Different regimes of pore coating are indentified, depending on the mode of end-segment attachment and on the ratio of D to the radius of gyration of the free polymer chains in solution Rg. These initial findings can be used as a guide for the preparation of actual polymer brushes inside ordered porous membranes by the “grafting to” approach.
Submicrometer resolution far field high sensitivity Kerr microscopy for in-plane magnetization detection
Authors: Wang C. H. , Yang Z.
Published: July 2009

We report that a far field magneto-optical system designed for detecting the off-plane magnetization in polar configuration can also detect the in-plane magnetization, while preserving the high sensitivity by using symmetric illumination and photoelastic modulation, even though the optical axis of the system is vertical to the sample surface. The spatial resolution can reach 500 nm at 514 nm in wavelength. The in-plane sensitivity can be eliminated by using an aperture to remove the off-axis obliquely incident light generated by the high numerical aperture objective lens that focuses the laser beam onto the sample surface.
Oxygen-ion-beam-driven electrostatic ion cyclotron instability of hydrogen plasma
Authors: Chibisov D. V. , Mikhailenko V. S. , Stepanov K. N.
Published: July 2009

The electrostatic ion cyclotron instability of hydrogen plasma driven by an oxygen ion beam and resulting turbulent heating of both ion species is investigated. The instability growth rate exceeds the oxygen ion gyrofrequency, so that the oxygen ions may be considered as unmagnetized during the process of waves growth. As a result the instability is developed due to inverse Landau damping of the ion cyclotron waves caused by thermal motion of oxygen ions across the magnetic field. The quasilinear analysis of the turbulent heating of both ion species resulted from their interactions with ion cyclotron turbulence indicates that this instability may be responsible for the observed anisotropic heating of auroral outflowing oxygen O+ ions in the ionosphere.
Viscous potential flow analysis of radial fingering in a Hele-Shaw cell
Authors: Kim Hyungjun , Funada Toshio , Joseph Daniel D. , Homsy G. M.
Published: July 2009

The problem of radial fingering in two phase gas/liquid flow in a Hele-Shaw cell under injection of gas is studied here. The fingers arise as an instability of a time-dependent flow. The instability is analyzed as a viscous potential flow, in which potential flow analysis of Paterson [L. Paterson, J. Fluid Mech. 113, 513 (1981)] and others is augmented to account for the effects of viscosity on the normal stress at the gas/liquid interface. The addition of these new effects brings our theory into a much better agreement with experiments of Maxworthy [T. Maxworthy, Phys. Rev. A 39, 5863 (1989)] than other theories.
Wetting and drying transitions in mean-field theory: Describing the surface parameters for the theory of Nakanishi and Fisher in terms of a microscopic model
Authors: Kuipers Joris , Blokhuis Edgar M.
Published: July 2009

The theory of Nakanishi and Fisher [Phys. Rev. Lett. 49, 1565 (1982)] describes the wetting behavior of a liquid and vapor phase in contact with a substrate in terms of the surface chemical potential h1 and the surface enhancement parameter g. Using density functional theory, we derive molecular expressions for h1 and g and compare with earlier expressions derived from Landau lattice mean-field theory. The molecular expressions are applied to compare with results from density functional theory for a square-gradient fluid in a square-well fluid-substrate potential and with molecular dynamics simulations.
Optofluidic circular grating distributed feedback dye laser
Authors: Chen Yan , Li Zhenyu , Henry M. David , Scherer Axel
Published: July 2009

We demonstrate an optically pumped surface emitting optofluidic dye laser using a second-order circular grating distributed feedback resonator. We present a composite bilayer soft lithography technique specifically developed for the fabrication of our dye laser and investigate a hybrid polymer material system [poly(dimethylsiloxane)/perfluoropolyether] to construct high-resolution Bragg gratings. Our lasers emit single frequency light at low lasing thresholds of 6 μJ/mm2. These optofluidic dye lasers can serve as low-cost and compact coherent light sources that are fully integrated within microfluidic analysis chips and provide an efficient approach to construct compact spectroscopy systems.
Growth and characterization of InAsN/GaAs dilute nitride semiconductor alloys for the midinfrared spectral range
Authors: de la Mare M. , Zhuang Q. , Krier A. , Patanè A. , Dhar S.
Published: July 2009

We report the growth of InAsN onto GaAs substrates using nitrogen plasma source molecular beam epitaxy. We describe the spectral properties of InAsN alloys with N-content in the range of 0%–1% and photoluminescence emission in the midinfrared spectral range. The photoluminescence emission of the sample containing 1% N reveals localized energy levels resonant with the conduction band states of InAsN.
Twinning partial multiplication at grain boundary in nanocrystalline fcc metals
Authors: Zhu Y. T. , Wu X. L. , Liao X. Z. , Narayan J. , Mathaudhu S. N. , Kecskés L. J.
Published: July 2009

Most deformation twins in nanocrystalline face-centered cubic (fcc) metals have been observed to form from grain boundaries. The growth of such twins requires the emission of Shockley partials from the grain boundary on successive slip planes. However, it is statistically improbable for a partial to exist on every slip plane. Here we propose a dislocation reaction and cross-slip mechanism on the grain boundary that would supply a partial on every successive slip plane for twin growth. This mechanism can also produce a twin with macrostrain smaller than that caused by a conventional twin.
Extension of the diffuse mismatch model for thermal boundary conductance between isotropic and anisotropic materials
Authors: Duda John C. , Smoyer Justin L. , Norris Pamela M. , Hopkins Patrick E.
Published: July 2009

This model is an extension of the diffuse mismatch model (DMM), tailored to accurately predict thermal boundary conductance (hBD) at interfaces where one material comprising the interface is characterized by high elastic anisotropy. Temperature-dependent specific heat is calculated with this vibrational model and compared to published values. Modifications to the DMM that incorporate the vibrational model are presented with predictions of hBD at a metal-graphite interface. This model slightly underestimates experimental data, as expected, as the large acoustic mismatch between metals and graphite suggests inelastic scattering, something the DMM does not take into account.
Bilateral visual field maps in a patient with only one hemisphere
Authors: Muckli Lars , Naumer Marcus J. , Singer Wolf
Published: July 2009

In mammals smooth retinotopic maps of the visual field are formed along the visual processing pathway whereby the left visual field is represented in the right hemisphere and vice versa. The reorganization of retinotopic maps in the lateral geniculate nucleus (LGN) of the thalamus and early visual areas (V1–V3) is studied in a patient who was born with only one cerebral hemisphere. Before the seventh week of embryonic gestation, the development of the patient's right cerebral hemisphere terminated. Despite the complete loss of her right hemisphere (di- and telencephalon) at birth, the patient's remaining hemisphere has not only developed maps of the contralateral (right) visual hemifield but, surprisingly, also maps of the ipsilateral (left) visual hemifield. Retinal ganglion-cells changed their predetermined crossing pattern in the optic chiasm and grew to the ipsilateral LGN. In the visual cortex, islands of ipsilateral visual field representations were located along the representations of the vertical meridian. In V1, smooth and continuous maps from contra- and ipsilateral hemifield overlap each other, whereas in ventral V2 and V3 ipsilateral quarter field representations invaded small distinct cortical patches. This reveals a surprising flexibility of the self-organizing developmental mechanisms responsible for map formation.
Parental stress increases the effect of traffic-related air pollution on childhood asthma incidence
Authors: Shankardass Ketan , McConnell Rob , Jerrett Michael , Milam Joel , Richardson Jean , Berhane Kiros
Published: July 2009

Exposure to traffic-related pollution (TRP) and tobacco smoke have been associated with new onset asthma in children. Psychosocial stress-related susceptibility has been proposed to explain social disparities in asthma. We investigated whether low socioeconomic status (SES) or high parental stress modified the effect of TRP and in utero tobacco smoke exposure on new onset asthma. We identified 2,497 children aged 5–9 years with no history of asthma or wheeze at study entry (2002–2003) into the Children's Health Study, a prospective cohort study in southern California. The primary outcome was parental report of doctor-diagnosed new onset asthma during 3 years of follow-up. Residential exposure to TRP was assessed using a line source dispersion model. Information about maternal smoking during pregnancy, parental education (a proxy for SES), and parental stress were collected in the study baseline questionnaire. The risk of asthma attributable to TRP was significantly higher for subjects with high parental stress (HR 1.51 across the interquartile range for TRP; 95% CI 1.16–1.96) than for subjects with low parental stress (HR 1.05, 95% CI 0.74–1.49; interactionPvalue 0.05). Stress also was associated with larger effects of in utero tobacco smoke. A similar pattern of increased risk of asthma was observed among children from low SES families who also were exposed to either TRP or in utero tobacco smoke. These results suggest that children from stressful households are more susceptible to the effects of TRP and in utero tobacco smoke on the development of asthma.
Ecosocial consequences and policy implications of disease management in East African agropastoral systems
Authors: Gutierrez Andrew Paul , Gilioli Gianni , Baumgärtner Johann
Published: July 2009

International research and development efforts in Africa have brought ecological and social change, but analyzing the consequences of this change and developing policy to manage it for sustainable development has been difficult. This has been largely due to a lack of conceptual and analytical models to access the interacting dynamics of the different components of ecosocial systems. Here, we examine the ecological and social changes resulting from an ongoing suppression of trypanosomiasis disease in cattle in an agropastoral community in southwest Ethiopia to illustrate how such problems may be addressed. The analysis combines physiologically based demographic models of pasture, cattle, and pastoralists and a bioeconomic model that includes the demographic models as dynamic constraints in the economic objective function that maximizes the utility of individual consumption under different level of disease risk in cattle. Field data and model analysis show that suppression of trypanosomiasis leads to increased cattle and human populations and to increased agricultural development. However, in the absence of sound management, these changes will lead to a decline in pasture quality and increase the risk from tick-borne diseases in cattle and malaria in humans that would threaten system sustainability and resilience. The analysis of these conflicting outcomes of trypanosomiasis suppression is used to illustrate the need for and utility of conceptual bioeconomic models to serve as a basis for developing policy for sustainable agropastoral resource management in sub-Saharan Africa.
Acoustically driven programmable liquid motion using resonance cavities
Authors: Langelier Sean M. , Chang Dustin S. , Zeitoun Ramsey I. , Burns Mark A.
Published: July 2009

Performance and utility of microfluidic systems are often overshadowed by the difficulties and costs associated with operation and control. As a step toward the development of a more efficient platform for microfluidic control, we present a distributed pressure generation scheme whereby independently tunable pressure sources can be simultaneously controlled by using a single acoustic source. We demonstrate how this scheme can be used to perform precise droplet positioning as well as merging, splitting, and sorting within open microfluidic networks. We further show how this scheme can be implemented for control of continuous-flow systems, specifically for generation of acoustically tunable liquid gradients. Device operation hinges on a resonance-decoding and rectification mechanism by which the frequency content in a composite acoustic input is decomposed into multiple independently buffered output pressures. The device consists of a bank of 4 uniquely tuned resonance cavities (404, 484, 532, and 654 Hz), each being responsible for the actuation of a single droplet, 4 identical flow-rectification structures, and a single acoustic source. Cavities selectively amplify resonant tones in the input signal, resulting in highly elevated local cavity pressures. Fluidic-rectification structures then serve to convert the elevated oscillating cavity pressures into unidirectional flows. The resulting pressure gradients, which are used to manipulate fluids in a microdevice, are tunable over a range of ≈0–200 Pa with a control resolution of 10 Pa.
Gain in sensitivity and loss in temporal contrast of STDP by dopaminergic modulation at hippocampal synapses
Authors: Zhang Ji-Chuan , Lau Pak-Ming , Bi Guo-Qiang
Published: July 2009

Spike-timing-dependent plasticity (STDP) is considered a physiologically relevant form of Hebbian learning. However, behavioral learning often involves action of reinforcement or reward signals such as dopamine. Here, we examined how dopamine influences the quantitative rule of STDP at glutamatergic synapses of hippocampal neurons. The presence of 20 μM dopamine during paired pre- and postsynaptic spiking activity expanded the effective time window for timing-dependent long-term potentiation (t-LTP) to at least −45 ms, and allowed normally ineffective weak stimuli with fewer spike pairs to induce significant t-LTP. Meanwhile, dopamine did not affect the degree of t-LTP induced by normal strong stimuli with spike timing (ST) of +10 ms. Such dopamine-dependent enhancement in the sensitivity of t-LTP was completely blocked by the D1-like dopamine receptor antagonist SCH23390, but not by the D2-like dopamine receptor antagonist sulpiride. Surprisingly, timing-dependent long-term depression (t-LTD) at negative ST was converted into t-LTP by dopamine treatment; this conversion was also blocked by SCH23390. In addition, t-LTP in the presence of dopamine was completely blocked by the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid, indicating that D1-like receptor-mediated modulation appears to act through the classical NMDA receptor-mediated signaling pathway that underlies STDP. These results provide a quantitative and mechanistic basis for a previously undescribed learning rule that depends on pre- and postsynaptic ST, as well as the global reward signal.
Duodenal acidity “sensing” but not epithelial HCO
3
−
supply is critically dependent on carbonic anhydrase II expression
Authors: Sjöblom Markus , Singh Anurag Kumar , Zheng Wen , Wang Jian , Tuo Bi-guang , Krabbenhöft Anja , Riederer Brigitte , Gros Gerolf , Seidler Ursula
Published: July 2009

Carbonic anhydrase (CA) is strongly expressed in the duodenum and has been implicated in a variety of physiological functions including enterocyte HCO
3
−
supply for secretion and the “sensing” of luminal acid and CO
2
. Here, we report the physiological role of the intracellular CAII isoform involvement in acid-, PGE
2,
and forskolin-induced murine duodenal bicarbonate secretion (DBS) in vivo. CAII-deficient and WT littermates were studied in vivo during isoflurane anesthesia. An approximate 10-mm segment of the proximal duodenum with intact blood supply was perfused under different experimental conditions and DBS was titrated by pH immediately. Two-photon confocal microscopy using the pH-sensitive dye SNARF-1F was used to assess duodenocyte pH
i
in vivo. After correction of systemic acidosis by infusion of isotonic Na
2
CO
3
, basal DBS was not significantly different in CAII-deficient mice and WT littermates. The duodenal bicarbonate secretory response to acid was almost abolished in CAII-deficient mice, but normal to forskolin- or 16,16-dimethyl PGE
2
stimulation. The complete inhibition of tissue CAs by luminal methazolamide and i.v. acetazolamide completely blocked the response to acid, but did not significantly alter the response to forskolin. While duodenocytes acidified upon luminal perfusion with acid, no significant pH
i
change occurred in CAII-deficient duodenum in vivo. The results suggest that CA II is important for duodenocyte acidification by low luminal pH and for eliciting the acid-mediated HCO
3
−
secretory response, but is not important in the generation of the secreted HCO
3
−
ions.
The titin-telethonin complex is a directed, superstable molecular bond in the muscle Z-disk
Authors: Bertz Morten , Wilmanns Matthias , Rief Matthias
Published: July 2009

Mechanical stability of bonds and protein interactions has recently become accessible through single molecule mechanical experiments. So far, mechanical information about molecular bond mechanics has been largely limited to a single direction of force application. However, mechanical force acts as a vector in space and hence mechanical stability should depend on the direction of force application. In skeletal muscle, the giant protein titin is anchored in the Z-disk by telethonin. Much of the structural integrity of the Z-disk hinges upon the titin-telethonin bond. In this paper we show that the complex between the muscle proteins titin and telethonin forms a highly directed molecular bond. It is designed to resist ultra-high forces if they are applied in the direction along which it is loaded under physiological conditions, while it breaks easily along other directions. Highly directed molecular bonds match in an ideal way the requirements of tissues subject to mechanical stress.
Maternally invested carotenoids compensate costly ectoparasitism in the hihi
Authors: Ewen John G. , Thorogood Rose , Brekke Patricia , Cassey Phillip , Karadas Filiz , Armstrong Doug P.
Published: July 2009

Dietary ingested carotenoid biomolecules have been linked to both improved health and immunity in nestling birds. Here, we test whether maternally invested egg carotenoids can offset the cost of parasitism in developing nestling hihi (Notiomystis cincta) from the bloodsucking mite (Ornithonyssus bursa). Our results reveal clear negative effects of parasitism on nestlings, and that maternally derived carotenoids compensate this cost, resulting in growth parameters and ultimate mass achieved being similar to nonparasitized young. Our results offer an unique example of a direct positive relationship between enhanced maternal investment of carotenoids and an ability to cope with a specific and costly parasite in young birds. AsO. bursainfestations reduce population viability in hihi, our findings also highlight the importance of key nutritional resources for endangered bird populations to better cope with common parasite infestations.
Induction of cerebral β-amyloidosis: Intracerebral versus systemic Aβ inoculation
Authors: Eisele Yvonne S. , Bolmont Tristan , Heikenwalder Mathias , Langer Franziska , Jacobson Laura H. , Yan Zheng-Xin , Roth Klaus , Aguzzi Adriano , Staufenbiel Matthias , Walker Lary C. , Jucker Mathias
Published: July 2009

Despite the importance of the aberrant polymerization of Aβ in the early pathogenic cascade of Alzheimer's disease, little is known about the induction of Aβ aggregation in vivo. Here we show that induction of cerebral β-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute Aβ-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced Aβ-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral β-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of Aβ-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral β-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral β-amyloidosis through the Aβ-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of β-amyloidosis. Our results suggest that minute amounts of Aβ-containing brain material in direct contact with the CNS can induce cerebral β-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to Aβ.
Mechanisms and feasibility of prey capture in ambush-feeding zooplankton
Authors: Kiørboe Thomas , Andersen Anders , Langlois Vincent J. , Jakobsen Hans Henrik , Bohr Tomas
Published: July 2009

Many marine zooplankters, particularly among copepods, are “ambush feeders” that passively wait for their prey and capture them by fast surprise attacks. This strategy must be very demanding in terms of muscle power and sensing capabilities, but the detailed mechanisms of the attacks are unknown. Using high-speed video we describe how copepods perform spectacular attacks by precision maneuvering during a rapid jump. We show that the flow created by the attacking copepod is so small that the prey is not pushed away, and that the attacks are feasible because of their high velocity (≈100 mm·s
−1
) and short duration (few ms), which leaves the prey no time for escape. Simulations and analytical estimates show that the viscous boundary layer that develops around the attacking copepod is thin at the time of prey capture and that the flow around the prey is small and remains potential flow. Although ambush feeding is highly successful as a feeding strategy in the plankton, we argue that power requirements for acceleration and the hydrodynamic constraints restrict the strategy to larger (> 0.25 mm), muscular forms with well-developed prey perception capabilities. The smallest of the examined species is close to this size limit and, in contrast to the larger species, uses its largest possible jump velocity for such attacks. The special requirements to ambush feeders with such attacks may explain why this strategy has evolved to perfection only a few times among planktonic suspension feeders (few copepod families and chaetognaths).
Leptin derived from adipocytes in injured peripheral nerves facilitates development of neuropathic pain via macrophage stimulation
Authors: Maeda Takehiko , Kiguchi Norikazu , Kobayashi Yuka , Ikuta Toshihiko , Ozaki Masanobu , Kishioka Shiroh
Published: July 2009

Nerve injury may result in neuropathic pain, characterized by allodynia and hyperalgesia. Accumulating evidence suggests the existence of a molecular substrate for neuropathic pain produced by neurons, glia, and immune cells. Here, we show that leptin, an adipokine exclusively produced by adipocytes, is critical for the development of tactile allodynia through macrophage activation in mice with partial sciatic nerve ligation (PSL). PSL increased leptin expression in adipocytes distributed at the epineurium of the injured sciatic nerve (SCN). Leptin-deficient animals,
ob/ob
mice, showed an absence of PSL-induced tactile allodynia, which was reversed by the administration of leptin to the injured SCN. Perineural injection of a neutralizing antibody against leptin reproduced this attenuation. Macrophages recruited to the perineurium of the SCN expressed the leptin receptor and phosphorylated signal transducer and activator of transcription 3 (pSTAT3), a transcription factor downstream of leptin. PSL also up-regulated the accepted mediators of neuropathic pain—namely, cyclooxygenase-2, inducible nitric oxide synthase, and matrix metalloprotease-9—in the injured SCN, with transcriptional activation of their gene promoters by pSTAT3. This up-regulation was partly reproduced in a macrophage cell line treated with leptin. Administration of peritoneal macrophages treated with leptin to the injured SCN reversed the failure of
ob/ob
mice to develop PSL-induced tactile allodynia. We suggest that leptin induces recruited macrophages to produce pronociceptive mediators for the development of tactile allodynia. This report shows that adipocytes associated with primary afferent neurons may be involved in the development of neuropathic pain through adipokine secretion.
Observation of water dangling OH bonds around dissolved nonpolar groups
Authors: Perera P. N. , Fega K. R. , Lawrence C. , Sundstrom E. J. , Tomlinson-Phillips J. , Ben-Amotz Dor
Published: July 2009

We report the experimental observation of water dangling OH bonds in the hydration shells around dissolved nonpolar (hydrocarbon) groups. The results are obtained by combining vibrational (Raman) spectroscopy and multivariate curve resolution (MCR), to reveal a high-frequency OH stretch peak arising from the hydration shell around nonpolar (hydrocarbon) solute groups. The frequency and width of the observed peak is similar to that of dangling OH bonds previously detected at macroscopic air–water and oil–water interfaces. The area of the observed peak is used to quantify the number of water dangling bonds around hydrocarbon chains of different length. Molecular dynamics simulation of the vibrational spectra of water molecules in the hydration shell around neopentane and benzene reveals high-frequency OH features that closely resemble the experimentally observed dangling OH vibrational bands around neopentyl alcohol and benzyl alcohol. The red-shift of ≈50 cm
−1
induced by aromatic solutes is similar to that previously observed upon formation of a π-H bond (in low-temperature benzene–water clusters).
Biological and immunological characteristics of hepatitis E virus-like particles based on the crystal structure
Authors: Yamashita Tetsuo , Mori Yoshio , Miyazaki Naoyuki , Cheng R. Holland , Yoshimura Masato , Unno Hideaki , Shima Ryoichi , Moriishi Kohji , Tsukihara Tomitake , Li Tian Cheng , Takeda Naokazu , Miyamura Tatsuo , Matsuura Yoshiharu
Published: July 2009

Hepatitis E virus (HEV) is a causative agent of acute hepatitis. The crystal structure of HEV-like particles (HEV-LP) consisting of capsid protein was determined at 3.5-Å resolution. The capsid protein exhibited a quite different folding at the protruding and middle domains from the members of the families of
Caliciviridae
and
Tombusviridae
, while the shell domain shared the common folding. Tyr-288 at the 5-fold axis plays key roles in the assembly of HEV-LP, and aromatic amino acid residues are well conserved among the structurally related viruses. Mutational analyses indicated that the protruding domain is involved in the binding to the cells susceptive to HEV infection and has some neutralization epitopes. These structural and biological findings are important for understanding the molecular mechanisms of assembly and entry of HEV and also provide clues in the development of preventive and prophylactic measures for hepatitis E.
Morphology and interaction between lipid domains
Authors: Ursell Tristan S. , Klug William S. , Phillips Rob
Published: July 2009

Cellular membranes are a heterogeneous mix of lipids, proteins and small molecules. Special groupings enriched in saturated lipids and cholesterol form liquid-ordered domains, known as “lipid rafts,” thought to serve as platforms for signaling, trafficking and material transport throughout the secretory pathway. Questions remain as to how the cell maintains small fluid lipid domains, through time, on a length scale consistent with the fact that no large-scale phase separation is observed. Motivated by these examples, we have utilized a combination of mechanical modeling and in vitro experiments to show that membrane morphology plays a key role in maintaining small domain sizes and organizing domains in a model membrane. We demonstrate that lipid domains can adopt a flat or dimpled morphology, where the latter facilitates a repulsive interaction that slows coalescence and helps regulate domain size and tends to laterally organize domains in the membrane.
Akt1 is critical for acute inflammation and histamine-mediated vascular leakage
Authors: Di Lorenzo Annarita , Fernández-Hernando Carlos , Cirino Giuseppe , Sessa William C.
Published: July 2009

Akt1 is implicated in cell metabolism, survival migration, and gene expression; however, little is known about the role of specific Akt isoforms during inflammation in vivo. Thus, we directly explored the roles of the isoforms Akt1 and Akt2 in acute inflammation models by using mice deficient in either Akt1 or Akt2.
Akt1
−/−
mice showed a markedly reduced edema versus
Akt2
−/−
and WT controls, and the reduced inflammation was associated with a dramatic decrease in neutrophil and monocyte infiltration. The loss of Akt1 did not affect leukocyte functions in vitro, and bone marrow transplant experiments suggest that host Akt1 regulates leukocyte emigration into inflamed tissues. Moreover, carrageenan-induced edema and the direct propermeability actions of bradykinin and histamine were reduced dramatically in
Akt1
−/−
versus WT mice. These findings are supported by in vitro experiments showing that Akt1 deficiency or blockade of nitric oxide synthase markedly reduces histamine-stimulated changes in transendothelial electrical resistance of microvascular endothelial cells. Collectively, these results suggest that Akt1 is necessary for acute inflammation and exerts its actions primarily via regulation of vascular permeability, leading to edema and leukocyte extravasation.
Neural transplants in patients with Huntington's disease undergo disease-like neuronal degeneration
Authors: Cicchetti F. , Saporta S. , Hauser R. A. , Parent M. , Saint-Pierre M. , Sanberg P. R. , Li X. J. , Parker J. R. , Chu Y. , Mufson E. J. , Kordower J. H. , Freeman T. B.
Published: July 2009

The clinical evaluation of neural transplantation as a potential treatment for Huntington's disease (HD) was initiated in an attempt to replace lost neurons and improve patient outcomes. Two of 3 patients with HD reported here, who underwent neural transplantation containing striatal anlagen in the striatum a decade earlier, have demonstrated marginal and transient clinical benefits. Their brains were evaluated immunohistochemically and with electron microscopy for markers of projection neurons and interneurons, inflammatory cells, abnormal huntingtin protein, and host-derived connectivity. Surviving grafts were identified bilaterally in 2 of the subjects and displayed classic striatal projection neurons and interneurons. Genetic markers of HD were not expressed within the graft. Here we report in patients with HD that (i) graft survival is attenuated long-term; (ii) grafts undergo disease-like neuronal degeneration with a preferential loss of projection neurons in comparison to interneurons; (iii) immunologically unrelated cells degenerate more rapidly than the patient's neurons, particularly the projection neuron subtype; (iv) graft survival is attenuated in the caudate in comparison to the putamen in HD; (v) glutamatergic cortical neurons project to transplanted striatal neurons; and (vi) microglial inflammatory changes in the grafts specifically target the neuronal components of the grafts. These results, when combined, raise uncertainty about this potential therapeutic approach for the treatment of HD. However, these observations provide new opportunities to investigate the underlying mechanisms involved in HD, as well as to explore additional therapeutic paradigms.