bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerosol chemical composition in New York state from integrated filter samples: Urban/rural and seasonal contrasts
Authors: Schwab James J. , Felton H. D. , Demerjian Kenneth L.
Published: June 2004

Filter samples have been collected and analyzed for chemical composition at a number of sites in New York state for more than 2 years. Because of the broad focus of the New York Environmental Protection Agency Supersite program, these sites include remote, rural, and urban sites in midsized and large cities. Calculated blanks and laboratory reported minimum detection limits (MDLs) for all measured species are presented. Data are averaged by location and season and presented for six sites throughout New York state. Data are presented for PM2.5 mass, sulfate, nitrate, ammonium and carbon, and selected metals and groups of trace elements. An approximate ion balance of the major inorganic ionic species is also calculated, which shows a predominately negative ion balance with the rural and remote sites being the most negative. In addition to chemical composition values in mass per unit volume (reported to ambient conditions), we also calculate ratios of the mass concentration values for five sites referenced to our site that is closest to background, Whiteface Mountain in the Adirondacks. By computing base ratios for the various chemical components and ratios of ratios referenced to mass concentrations, we can provide some insight into the sources of these chemical components relative to the sources of PM2.5 mass. The ratio of ratios analysis indicated that sulfate and potassium are the most regional species considered and that EC and some metal species have the strongest urban (especially New York City) sources.
Phyllosilicate mineral assemblages of the SAFOD Pilot Hole and comparison with an exhumed segment of the San Andreas Fault System
Authors: Solum John G. , van der Pluijm Ben A.
Published: June 2004

This paper establishes a reference phyllosilicate data set from the SAFOD Pilot Hole for future SAFOD drilling and presents an application of these data for studies of exhumed fault segments. The chlorite assemblages in cuttings from two intervals of the SAFOD Pilot Hole are separated into two populations based on X‐ray diffraction characteristics. The first population is found in granite in both the deeper and shallower interval, whereas the second population occurs only in clastic sedimentary rocks in the shallower interval. The characteristics of the first population match those for protolith and cataclasite of the exhumed Punchbowl Fault, whereas samples from intensely deformed ultracataclasite are most similar to the second. This supports previous findings that the mineral assemblages in the ultracataclasite formed after the cessation of motion along the fault, above a depth of ∼2 km, and that mineral assemblages in these exhumed fault rocks have been overprinted by post‐faulting alteration.
Origin of ELF/ULF waves triggered by positive cloud to ground lightning above mesoscale connective systems
Authors: Sorasio G. , Shukla P. K. , Resendes D. P. , Mendonça J. T.
Published: June 2004

Powerful electric currents and transient luminous events (sprites, blue jets and gigantic jets) have been detected in discharges between thunderclouds and the lower Ionosphere. The occurrence of such phenomena is strongly related to the occurrence of Ultra Low Frequency (ULF ∼ 6–50 Hz) waves and to the occurrence of positive polarity cloud‐to‐ground flashes. In the present letter, we present a novel mechanism to explain the origin and propagation of the observed ULF waves. Ionospheric clouds are composed of charged ice/smoke particulates, protons, electrons and neutrals. Our objective here is to show that such partially ionized dusty plasmas with streaming electrons in ionospheric clouds may support unstable ULF dust acoustic waves (DAWs). For our purposes, we employ a multifluid dusty plasma model and derive the dispersion relation for modified DAWs in a magnetized collisional plasma. The dispersion relation is analyzed numerically to obtain the growth rate and threshold.
Transient ion beamlet injections into spatially separated PSBL flux tubes observed by Cluster‐CIS
Authors: Keiling A. , Rème H. , Dandouras I. , Bosqued J. M. , Parks G. K. , McCarthy M. , Kistler L. , Amata E. , Klecker B. , Korth A. , Lundin R.
Published: June 2004

Ion measurements from Cluster‐CIS were used to characterize and interpret the signatures of PSBL energy‐dispersed ions and their fine structure. On 14 February 2001, several ion injections were encountered by SC 1 and SC 3, separated by ∼530 km, during an outbound orbit at 4.5 RE. Both satellites recorded the same ion structures. The energy dispersion of each ion structure was dominated by the time‐of‐flight effect (TDIS). In addition, we show evidence for spatial properties of the ion injections: (1) SC 1 and SC 3 encountered the same ion structures with a time delay of ∼30 s, which indicates their spatial extent. (2) The peak energy of each injection increased with increasing latitude. We propose a scenario in which both temporal and spatial effects are incorporated: Ion beamlets are impulsively and recurrently injected from separated regions distributed along the tail current sheet (ranging from X ∼70 to 110 RE) into latitudinally narrow (∼600 km to 1800 km) and convecting (at ∼10 km/s) flux tubes of the PSBL. Beamlets injected closer to the X line gain higher energies as a result of the intrinsic dispersion effect.
Does the level of chronic physical activity alter heart rate variability in healthy older women?
Authors: RELAND Sylvia , VILLE Nathalie S. , WONG Sara , SENHADJÏ Lotfi , CARRÉ François
Published: June 2004

In the present study, we investigated the effects of three levels of chronic physical activity on HRV (heart rate variability) in healthy older women. ECG recordings were taken in three (low-, moderate- and high-) activity groups in supine position with free and with controlled breathing, and during orthostatic stress. Temporal and spectral HRV indices were obtained from the ECG signal processing. The main results showed that, in supine position with free and controlled breathing, the HF (high-frequency) spectral component (P<0.01) and the rMSSD (square root of the mean squared differences) between two adjacent RR intervals (P<0.05 and P<0.01 respectively) were elevated in the high-activity group compared with the low-activity group. No significant difference was observed between groups during the orthostatic test. Within groups, in the supine position, the change from free to controlled breathing produced a decrease in the LF (low-frequency) spectral component in all three groups (P<0.01). The change from supine to standing position produced a decrease in RR in all three groups (P<0.05 in low- and moderate-activity groups, and P<0.01 in high-activity group); the rMSSD and the HF spectral component decreased only in the high-activity group (P<0.01). In conclusion, this study performed on older women showed that parasympathetic indices of resting HRV were significantly elevated in a high physical activity group compared with in a low physical activity group. Furthermore, parasympathetic indices of HRV decreased during an orthostatic test only in the high-activity group. The influence of chronic moderate physical activity on HRV in older women was small in the present study.
Stroke and blood pressure variability
Authors: PEPPERELL Justin C. T.
Published: June 2004

Sleep apnoea is associated with increased cardiovascular risk. Sleep apnoea is common after stroke and associated with increased blood pressure variability as described by Turkington and co-workers in this issue of Clinical Science. Both sleep apnoea and blood pressure variability confer a poor prognosis after stroke and are potentially treatable. Many studies of CPAP (continuous positive airway pressure) demonstrate decreases in cardiovascular risk markers in other patient groups. Although difficult to apply in these patients in the short term, CPAP has some potential benefits in medium-term rehabilitation and secondary prevention following stroke, which warrants further study.
Ensemble-averaging in dynamic light scattering by an echo technique
Authors: Pham K. N. , Egelhaaf S. U. , Moussaı̈d A. , Pusey P. N.
Published: June 2004

We describe a development of dynamic light scattering which allows accurate measurement of relaxation processes in slowly relaxing or nonergodic samples. The sample is rotated continuously while measuring the scattered intensity; the time correlation function of the intensity obtained in this way contains peaks, or “echoes,” at multiples of the rotational period, whose heights follow the sample’s properly ensemble-averaged dynamics. We analyze the method with a simple theoretical model and confirm it by computer simulation. Theory and simulation show that the profiles of the peaks are not affected by the sample’s dynamics; this allows correction to be made for imperfect rotation of the sample. We present experimental data from a rigid and a fluid sample, showing that the method can produce very precise results. Being able to measure dynamics over relaxation times ranging from 1 to beyond 104 s with measurement time comparable to the maximum delay time, this method has large potential in a wide range of applications where the dynamics of slowly relaxing or nonergodic samples are of interest. The echo technique can be implemented with simple hardware on almost any light scattering setup.
Comprehensive study of noise processes in electrode electrolyte interfaces
Authors: Hassibi Arjang , Navid Reza , Dutton Robert W. , Lee Thomas H.
Published: June 2004

A general circuit model is derived for the electrical noise of electrode–electrolyte systems, with emphasis on its implications for electrochemical sensors. The noise power spectral densities associated with all noise sources introduced in the model are also analytically calculated. Current and voltage fluctuations in typical electrode–electrolyte systems are demonstrated to originate from either thermal equilibrium noise created by conductors, or nonequilibrium excess noise caused by charge transfer processes produced by electrochemical interactions. The power spectral density of the thermal equilibrium noise is predicted using the fluctuation-dissipation theorem of thermodynamics, while the excess noise is assessed in view of charge transfer kinetics, along with mass transfer processes in the electrode proximity. The presented noise model not only explains previously reported noise spectral densities such as thermal noise in sensing electrodes, shot noise in electrochemical batteries, and 1/f noise in corrosive interfaces, it also provides design-oriented insight into the fabrication of low-noise micro- and nanoelectrochemical sensors.
Selective infrared photodissociation of protonated para-fluorophenol isomers: Substitution effects in oxonium and fluoronium ions
Authors: Solcà Nicola , Dopfer Otto
Published: June 2004

Isomer-selective infrared photodissociation (IRPD) spectra are obtained for the first time for protonated polyfunctional aromatic molecules isolated in the gas phase. IRPD spectra of the oxonium and fluoronium isomers of protonated para-fluorophenol (C6H6FO+) were separately obtained by monitoring resonant photo-induced H2O and HF loss, respectively. Analysis of the F–H, O–H, and C–H stretch wave numbers provides valuable spectroscopic information on the chemical properties of these reactive intermediates, in particular on the substitution effects of functional groups.
Free energy perturbation study of water dimer dissociation kinetics
Authors: Ming Yi , Lai Geeling , Tong Chinghang , Wood Robert H. , Doren Douglas J.
Published: June 2004

An efficient approach is described for using accurate ab initio calculations to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. The feasibility of the method is demonstrated in an application to evaporation rates of water dimer at 230 K. The method, known as ABC-FEP (ab initio/classical free energy perturbation), begins with a calculation of the potential of mean force for the dissociation (evaporation) of small water clusters using a molecular dynamics (MD) simulation with a model potential. The free energy perturbation is used to calculate how changing from the model potential to a potential calculated from ab initio methods would alter the potential of mean force. The difference in free energy is the Boltzmann-weighted average of the difference between the ab initio and classical potential energies, with the average taken over a sample of configurations from the MD simulation. In principle, the method does not require a highly accurate model potential, though more accurate potentials require fewer configurations to achieve a small sampling error in the free energy perturbation step. To test the feasibility of obtaining accurate potentials of mean force from ab initio calculations at a modest number of configurations, the free energy perturbation method has been used to correct the errors when some standard models for bulk water (SPC, TIP4P, and TIP4P⋅FQ) are applied to water dimer. To allow a thorough exploration of sampling issues, a highly accurate fit to results of accurate ab initio calculations, known as SAPT-5s, as been used a proxy for the ab initio calculations. It is shown that accurate values for a point on the potential of mean force can be obtained from any of the water models using ab initio calculations at only 50 configurations. Thus, this method allows accurate simulations of small clusters without the need to develop water models specifically for clusters.
Hydrodynamic transport models for an ultrathin base Si bipolar transistor
Authors: Muscato Orazio
Published: June 2004

Hydrodynamic models for carrier transport in semiconductors can be derived by taking moments of the Boltzmann transport equation. The maximum entropy principle allows us to obtain a closed hydrodynamic model, containing no free parameters, in order to describe transport phenomena under conditions very far from thermodynamic equilibrium. Under suitable scaling assumptions, the above model reduces to the energy transport model, to the Navier-Stokes-Fourier model, or to the drift diffusion one, in which all the transport coefficients are now explicitly determined. In this paper we study the applicability of these models to an ultrathin base npn silicon bipolar transistor where the transport is quasiballistic. The validity of the constitutive equations for the fluxes and the production terms (which are the moments over the collisional operator) is investigated by using Monte Carlo simulations.
Investigation of phase transition in ferroelectric Pb0.70Sr0.30TiO3 thin films
Authors: Pontes F. M. , Leal S. H. , Leite E. R. , Longo E. , Pizani P. S. , Chiquito A. J. , Varela J. A.
Published: June 2004

We have carried out dielectric and Raman spectroscopy studies at the 298–623 K temperature range in polycrystalline Pb0.70Sr0.30TiO3 thin films grown by a soft chemical method. The diffuse phase-transition behavior of the thin films was observed by means of the dielectric constant versus temperature curves, which show a broad peak. Such behavior was confirmed later by Raman spectroscopy measurements up to 823 K, indicating that a diffuselike phase transition takes place at around 548–573 K. The damping factor of the E(1TO) soft mode was calculated using the damped simple harmonic oscillator model. On the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of a breakdown of the microscopic local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broad bands at some temperature interval above the ferroelectric-paraelectric phase-transition temperature suggested a diffuse nature of the phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in this thin film.
Asymptotic correction of the exchange–correlation kernel of time-dependent density functional theory for long-range charge-transfer excitations
Authors: Gritsenko Oleg , Baerends Evert Jan
Published: June 2004

Time-dependent density functional theory (TDDFT) calculations of charge-transfer excitation energies ωCT are significantly in error when the adiabatic local density approximation (ALDA) is employed for the exchange–correlation kernel fxc. We relate the error to the physical meaning of the orbital energy of the Kohn–Sham lowest unoccupied molecular orbital (LUMO). The LUMO orbital energy in Kohn–Sham DFT—in contrast to the Hartree–Fock model—approximates an excited electron, which is correct for excitations in compact molecules. In CT transitions the energy of the LUMO of the acceptor molecule should instead describe an added electron, i.e., approximate the electron affinity. To obtain a contribution that compensates for the difference, a specific divergence of fxc is required in rigorous TDDFT, and a suitable asymptotically correct form of the kernel fxcasymp is proposed. The importance of the asymptotic correction of fxc is demonstrated with the calculation of ωCT(R) for the prototype diatomic system HeBe at various separations R(He–Be). The TDDFT–ALDA curve ωCT(R) roughly resembles the benchmark ab initio curve ωCTCISD(R) of a configuration interaction calculation with single and double excitations in the region R=1–1.5 Å, where a sizable He–Be interaction exists, but exhibits the wrong behavior ωCT(R)≪ωCTCISD(R) at large R. The TDDFT curve obtained with fxcasymp however approaches ωCTCISD(R) closely in the region R=3–10 Å. Then, the adequate rigorous TDDFT approach should interpolate between the LDA/GGA ALDA xc kernel for excitations in compact systems and fxcasymp for weakly interacting fragments and suitable interpolation expressions are considered.
Efficient and reliable numerical integration of exchange-correlation energies and potentials
Authors: Köster Andreas M. , Flores-Moreno Roberto , Reveles J. Ulises
Published: June 2004

An adaptive numerical integrator for the exchange-correlation energy and potential is presented. It uses the diagonal elements of the exchange-correlation potential matrix as a grid generating function. The only input parameter is the requested grid tolerance. In combination with a defined cell function the adaptive grid generation scales almost linear with the number of basis functions in a system. With the adaptive numerical integrator the self-consistent field energy error, which is due to the numerical integration of the exchange-correlation energy, converges with increasing adaptive grid size to a reference value. The performance of the adaptive numerical integration is analyzed using molecules with first, second, and third row elements. Especially for transition metal systems the adaptive numerical integrator shows considerably improved performance and reliability.
Tracing the phase diagram of the four-site water potential (TIP4P)
Authors: Sanz E. , Vega C. , Abascal J. L. F. , MacDowell L. G.
Published: June 2004

We present here the phase diagram for one of the most popular water models, the four-point transferable intermolecular potential (TIP4P) model. We show that TIP4P model, does indeed provide a qualitatively correct description of the phase diagram of water. The melting line of the five-point transferable intermolecular potential (TIP5P) at low pressures is also presented.
Higher order and infinite Trotter-number extrapolations in path integral Monte Carlo
Authors: Brualla L. , Sakkos K. , Boronat J. , Casulleras J.
Published: June 2004

Improvements beyond the primitive approximation in the path integral Monte Carlo method are explored both in a model problem and in real systems. Two different strategies are studied: The Richardson extrapolation on top of the path integral Monte Carlo data and the Takahashi-Imada action. The Richardson extrapolation, mainly combined with the primitive action, always reduces the number-of-beads dependence, helps in determining the approach to the dominant power law behavior, and all without additional computational cost. The Takahashi-Imada action has been tested in two hard-core interacting quantum liquids at low temperature. The results obtained show that the fourth-order behavior near the asymptote is conserved, and that the use of this improved action reduces the computing time with respect to the primitive approximation.
Percolation-to-droplets transition during spinodal decomposition in polymer blends, morphology analysis
Authors: Demyanchuk I. , Wieczorek S. A. , Hołyst R.
Published: June 2004

Phase separation kinetics of the off-critical mixture of polystyrene and poly(methylphenylsiloxane) is studied by the time-resolved light scattering and optical microscopy. The results from the light scattering experiments are correlated with the images obtained by the optical microscopic observation in order to find characteristic features of the scattering intensity during the percolation-to-droplets morphology transition. At the beginning of the spinodal decomposition process only a bicontinuous network is present in the system and the light scattering intensity has only one peak. The network coarsens and at the same time small droplets appear in the system resulting in a growth of the scattering intensity at very small wave vectors. When the large network starts to break up into disjoint elongated domains a second peak in the scattering intensity appears. Finally, both peaks merge into a single peak at zero wave vector, indicating a complete transformation of elongated domains into spherical droplets of variable sizes. The comparison of the direct microscopic observations with the light scattering spectra shows that the process of breaking up of the bicontinuous network starts when the growth of the first peak, corresponding to the bicontinuous pattern, becomes very slow (essentially pinned down).
Chain elongation suppression of cyclic block copolymers in lamellar microphase-separated bulk
Authors: Matsushita Y. , Iwata H. , Asari T. , Uchida T. , ten Brinke G. , Takano A.
Published: June 2004

Chain elongation suppression of cyclic block copolymers in microphase-separated bulk was determined quantitatively. Solvent-cast and annealed films are confirmed to show alternating lamellar structure and their microdomain spacing D increases with increasing total molecular weight M according to the relationship D∝M0.59, which agrees quite consistently with the theoretically predicted power law, i.e., D∝M3/5. This result is in contrast to the well-established issue for linear block copolymers, where the relationship D∝M2/3 has been confirmed to hold both experimentally and theoretically. This means that chain elongation of each component block is suppressed considerably, owing to their looped conformation in strongly segregated bulk.
Theory of bulk, surface and interface phase transition kinetics in thin films
Authors: Backus Ellen H. G. , Bonn Mischa
Published: June 2004

We report a theoretical study of phase transition kinetics in confined two-dimensional systems, motivated by recent experimental results on the amorphous-to-crystalline transition in supported, thin amorphous water films [E.H.G. Backus, M.L. Grecea, A.W. Kleyn, and M. Bonn, Phys. Rev. Lett. (to be published)]. We generalize and extend existing theories to simultaneously describe the converted (crystalline) fractions in the bulk, at the sample-vacuum surface, and at the sample-support interface as a function of time. The general approach presented here results in expressions for the time-dependent converted bulk, surface, and interface fractions, for arbitrary desorption rate from the thin film, nucleation and growth rates and also includes finite nucleation grain size. The converted bulk, surface, and interface fractions are calculated for nucleation of the new phase occurring (i) in the bulk, (ii) at the support-sample interface, and (iii) at the sample surface (sample-vacuum interface), resulting in nine expressions. The results demonstrate the advantage of monitoring bulk, surface and interface fractions simultaneously to make definite statements regarding the location of the nucleation, and to reliably determine the values of the relevant crystallization parameters.
Distribution functions for filaments under tension
Authors: Kessler David A. , Rabin Yitzhak
Published: June 2004

We develop a biased Monte Carlo simulation technique to measure the distribution functions of the extension and the end-to-end distance of fluctuating filaments stretched by external force. The method is applicable for arbitrary ratio of the persistence length to the contour length and for arbitrary forces, and also for the case of steric constraints, such as an external wall. The fundamental idea underlying the algorithm is to account explicitly for the length-scale dependence of the effective elastic moduli. We find that orientational fluctuations and wall effects produce non-Gaussian distributions for nearly rigid filaments in the small to intermediate force regime. The simulation results are tested against analytic expressions for the force-extension curves, both in the semiflexible and nearly stiff limits.
Normal-incidence InAs/In0.15Ga0.85As quantum dots-in-a-well detector operating in the long-wave infrared atmospheric window (8–12 μm)
Authors: Raghavan S. , Forman D. , Hill P. , Weisse-Bernstein N. R. , von Winckel G. , Rotella P. , Krishna S. , Kennerly S. W. , Little J. W.
Published: June 2004

Normal incidence InAs/In0.15Ga0.85As dots-in-a-well (DWELL) detectors are reported in which the peak operating wavelength was tailored from 7.2 to 11 μm using heterostructure engineering of the DWELL structure. Using an optimized design, a detector with a spectral response spanning the long-wave infrared atmospheric window (8–12 μm) is obtained. Spectral response peaks were observed at λp=10.3 μm and 11.3 μm under positive and negative bias, respectively. These peaks are attributed to bound-to-bound transitions from the InAs quantum dot to the InGaAs well.
Creation of SiOF films with SiF4/O2 plasmas: From gas-surface interactions to film formation
Authors: Zhang Jianming , Fisher Ellen R.
Published: June 2004

Fluorinated SiO2 (SiOF) films have been studied because of their relatively low dielectric constant and their potential as a replacement for SiO2 in the microelectronics industry. Despite the intense scrutiny, many of the details of the mechanisms for SiOF film deposition remain unclear. Here, we examined the macroscopic and molecular level chemistry of SiOF film deposition using SiF4/O2 plasmas. In the film formation studies, the plasma parameters of SiF4 fraction in the feed gases, F, defined as SiF4/(SiF4+O2), and applied rf power (P) were examined as well as the effects of ion bombardment and substrate temperature on film deposition. Fluorine incorporation in the film increases with both F and P. Film-deposition rate also increases with P, whereas its dependence on F is more complex. Ion bombardment decreases the film deposition rate and affects film composition significantly. On the molecular level, we examined the surface reactivity of SiF and SiF2 during SiOF film deposition using the imaging of radicals interacting with surfaces technique. SiF2 shows significant surface production during film deposition. The scattering coefficient S varies from 1.63±0.07 to 2.01±0.07. In contrast, SiF shows high surface reactivity R (defined as 1−S for S⩽1), which varies from 0.96±0.13 to 0.73±0.09, depending on plasma parameters. The surface interactions of SiF and SiF2, along with plasma gas-phase composition, were correlated with film characteristics to reveal possible film-deposition mechanisms.
Contribution of hole trap to persistent photoconductivity in n-type GaN
Authors: Cai S. , Parish G. , Dell J. M. , Nener B. D.
Published: June 2004

The transient behavior of persistent photoconductivity (PPC) in unintentionally doped GaN has been investigated for different excitation intensities and at different temperatures. The observed PPC buildup behavior can be described by a sum of two exponential functions with a long and a short time constant, which are attributed separately to the contributions of an electron trap and a hole trap, respectively. The concentrations of the electron trap and hole trap at 300 K are 1.6×1015 and 2.6×1015 cm−3, with a thermal activation energy level of 195.5 and 111.6 meV, respectively. Temperature dependence of the PPC buildup processes indicates that from 340 K down to about 240 K the rate parameters associated with the PPC buildup are dominated by the thermally activated capture mechanisms of defects. In contrast they are nearly independent of temperature below 240 K.
Colossal magnetoresistance in spinel type Zn1−xNixFe2O4
Authors: Akther Hossain A. K. M. , Seki M. , Kawai T. , Tabata H.
Published: June 2004

Spinel-type ferrites are widely used in practical applications. A fascinating property of Zn-Ni ferrites which reveals a direction for application is reported. A large negative magnetoresistance effect has been observed in ZnFe2O4 and Ni substituted Zn1−xNixFe2O4 ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature and a spin (cluster) glass transition was found for some compositions at low temperatures. The magnetoresistance is either parabolic or linear with respect to applied field up to 9 T depending on the compositions and temperatures. It was found that the magnetoresistance effect increases as the Ni content increases in Zn1−xNixFe2O4 up to x=0.2 and then again decreases and finally become negligible for x=1.0, i.e., NiFe2O4. This magnetoresistance effect can be explained with the help of spin-dependent scattering and the Yafet-Kittel angle of the Ni-substituted Zn-Ni ferrites.
Large magnetocaloric effect in a La0.7Ca0.3MnO3 single crystal
Authors: Phan Manh-Huong , Yu Seong-Cho , Hur Nam Hwi , Jeong Yoon-Hee
Published: June 2004

We report the results of a thorough study of the magnetocaloric effect (MCE) in a La0.7Ca0.3MnO3 single crystal, which undergoes a first-order magnetic phase transition at ∼227 K. The magnetic entropy change ΔSM and the adiabatic temperature change ΔTad reach, respectively, ∼6.42 J/kg K and 4.76 K for ΔB=5 T and even if both are smaller than those exhibited by gadolinium (∼9.8 J/kg K and ∼11.7 K), the ΔSM distribution here is much more uniform than that of gadolinium and polycrystalline manganites. This is desirable for an Ericson-cycle magnetic refrigerator. The MCE is larger in the single-crystalline manganite compared to the polycrystalline one. The manganite single crystal has large ΔSM induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. All these make the lanthanum manganite single crystal an attractive candidate as a working substance for AMR. The molecular field model provides a fairly good description of the magnetic entropy change at temperatures close to the Curie temperature.
Chiral exciton wave functions in cylindrical J aggregates
Authors: Didraga Cătălin , Knoester Jasper
Published: June 2004

We study the exciton wave functions and the optical properties of cylindrical molecular aggregates. The cylindrical symmetry allows for a decomposition of the exciton Hamiltonian into a set of effective one-dimensional Hamiltonians, characterized by a transverse wave number k2. These effective Hamiltonians have interactions that are complex if the cylinder exhibits chirality. We propose analytical ansätze for the eigenfunctions of these one-dimensional problems that account for a finite cylinder length, and present a general study of their validity. A profound difference is found between the Hamiltonian for the transverse wave number k2=0 and those with k2≠0. The complex nature of the latter leads to chiral wave functions, which we characterize in detail. We apply our general formalism to the chlorosomes of green bacteria and compare the wave functions as well as linear optical spectra (absorption and dichroism) obtained through our ansätze with those obtained by numerical diagonalization as well as those obtained by imposing periodic boundary conditions in the cylinder’s axis direction. It is found that our ansätze, in particular, capture the finite-length effect in the circular dichroism spectrum much better than the solution with periodic boundary conditions. Our ansätze also show that in finite-length cylinders seven superradiant states dominate the linear optical response.
The effect of a uniform radial electric field on the toroidal ion temperature gradient mode
Authors: Peeters A. G. , Strintzi D.
Published: June 2004

It has been shown [Maccio, Phys. Plasmas 8, 895 (2001)] that a uniform radial electric field can stabilize the toroidal ion temperature gradient mode in tokamak plasmas. In this paper, using the ballooning transform, the mechanism leading to stabilization is further clarified. However, the stabilizing effect depends on the choice of the background distribution function. It is shown that if the electric field is connected with a toroidal plasma rotation the stabilizing effect becomes ineffective. Consequently, in many current experiments this effect should not play a role.
Dependence of leakage current on dislocations in GaN-based light-emitting diodes
Authors: Li D. S. , Chen H. , Yu H. B. , Jia H. Q. , Huang Q. , Zhou J. M.
Published: June 2004

The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.
Lanthanum-based manganite films on MgO using SrTiO3 as a template layer
Authors: Pradhan A. K. , Sahu D. R. , Roul B. K. , Feng Y.
Published: June 2004

We report on the processing and characterization of high performance epitaxial manganite films grown on SrTiO3 and SrTiO3 buffered MgO substrates with a Tc tailored to room temperature. We have demonstrated that La1−xBaxMnO3 and La1−xSrxMnO3 epitaxial films on SrTiO3 buffered MgO substrate show significantly improved transport and magnetization properties in the vicinity of room temperature on ex situ annealing at 900 °C. Our results suggest that manganite films can be grown on either SrTiO3 or SrTiO3 buffered MgO substrates which can serve as template layer to integrate manganites onto appropriate semiconductors for device applications.
Experimental station for gas phase fluorescence spectroscopy
Authors: Stankiewicz M. , Garcı́a E. Melero , Ruiz J. Álvarez , Erman P. , Hatherly P. A. , Kivimäki A. , Rachlew E. , Rius i Riu J.
Published: June 2004

The details of an experimental setup for gas phase atomic and molecular fluorescence measurements using synchrotron radiation are described in this article. The most significant part of the apparatus is an optical arrangement, which allows for simultaneous measurements of dispersed as well as total fluorescence intensity using an effusive gas jet and an inbuilt gas cell assembled in a convenient plug and measure configuration. The first measurements concerning fluorescence of the N2 molecule around the N 1s edge obtained with this setup are presented.
Exploring molecular complexity: Conical intersections and NH3 photodissociation
Authors: Yarkony David R.
Published: June 2004

The role of conical intersections in the photodissociation of the Ã 1A2″ state of NH3 is investigated using extended atomic basis sets and a configuration state function expansion of approximately 8.5 million terms. A previously unknown portion of the 1 1A–2 1A seam of conical intersections with only Cs symmetry is located. This portion of the seam is readily accessible from the equilibrium geometry of the Ã 1A2″ state. These conical intersections are expected to play a role in the competition between adiabatic and nonadiabatic pathways for NH3(Ã 1A2″) photodissociation.
The in situ relationships between season of hatching, growth and condition in the southern calamary, Sepioteuthis australis
Authors: Pecl Gretta
Published: June 2004

This paper examines seasonal patterns in growth and condition of Sepioteuthis australis from temperate waters of Tasmania, Australia. Growth was described by a power function and was fast for a temperate species, with an average rate over the lifetime of 4–5% BW day–1. Sepioteuthis australis is an annual species, however spawning and hatching of juveniles appears to occur all year round. Analysis of individual juvenile growth demonstrated a correlation between seasonally increasing temperatures and progressively faster growth. Season of hatching also had a clear effect on adult growth; summer-hatched individuals were larger at 170–190 days of age compared with winter-hatched individuals (1002 ± 98 g and 632 ± 27 g respectively). The length–mantle weight relationship of adults was also dependent on season of hatching, with individuals hatched in summer and spring having heavier mantles at a given length than those hatched in winter or autumn. Differential rates of growth or varying levels of condition, or perhaps both, may affect the survivorship of individuals. Growth, condition and potentially lifespan of S. australis are dependent on environmental factors, with the dynamic nature of oceanographical conditions on the east coast of Tasmania resulting in a highly variable and fluctuating population structure.
The Bosnian Muslims and Albanians: Islam and Nationalism
Authors: Babuna Aydin
Published: June 2004

The drastic changes in the Balkans in the 1990s and the disintegration of Yugoslavia in particular have resulted in a large number of publications attempting to explain the break-up of this country and the political developments in the Balkans. Some of these publications deal partly with the local Muslims who were engaged in the Balkan conflicts but, with some exceptions, they are focused mainly on recent developments, with less attention paid to the historical contexts in which the Muslim nationalist movements were shaped.
Rag Doll Nations and the Politics of Differentiation on Arbitrary Borders: Karelia and Moldova*
Authors: Schrad Mark Lawrence
Published: June 2004

“Tell a man today to go and build a state,” Samuel Finer once stated, “and he will try to establish a definite and defensible boundary and compel those who live inside it to obey him.” While at best an oversimplification, Finer's insight illuminates an interesting aspect of state-society relations. Who is it that builds the state? How and where do they establish territorial boundaries, and how are those who live within that territory compelled to obey? Generally speaking, these are the questions that will be addressed here. Of more immediate concern is the fate of peoples located in regions where arbitrary land boundaries fall. Are they made loyal to the state through coercion or by their own compulsions? More importantly, how are their identities shaped by the efforts of the state to differentiate them from their compatriots on the other side of the borders? How is the shift from ethnic to national identities undertaken? A parallel elaboration of the national histories of the populations of Karelia and Moldova will shed light on these questions. The histories of each group are marked by a myriad of attempts to differentiate the identity of each ethnic community from their compatriots beyond the state's borders. The results of such overt, state-initiated efforts to differentiate borderland populations by encouraging a national identity at the expense of the ethnic, has ranged from the mundane to the tragic—from uneventful assimilation to persecution and even genocide. As an illustration of the range of possibilities and processes, I maintain that the tragedies of Karelia and Moldova are not exceptional, but rather are a consequence of their geographical straddling of arbitrary borders, and the need for the state to promote a distinctive national identity for these populations to differentiate them socially from their compatriots beyond the frontier.
Visual impairment and ocular abnormalities in children with fetal alcohol syndrome
Authors: Strömland Kerstin
Published: June 2004

Children with fetal alcohol syndrome (FAS) may have impaired vision and various ocular abnormalities. All parts of the eye may be affected and anomalies such as microphthalmus, microcornea, Peters' anomaly, cataract, persistent hyperplastic primary hyaloid vitreous body, coloboma of the iris and choroid, retinal dysplasia and, most commonly, optic nerve hypoplasia and tortuosity of the retinal vessels, have been reported. The periocular facial features consist of short palpebral fissures (included in the criteria for diagnosis of FAS), telecanthus, epicanthus and blepharoptosis. Visual function may be reduced to a moderate or severe degree. Refractive errors and strabismus are common. Considering the high frequency of ocular pathology in FAS, an ophthalmological examination is helpful in making the diagnosis. The early detection of impaired vision and ocular abnormalities in affected children is important in the management of the disorder. In this article, the ophthalmological signs and symptoms in children with FAS are presented.
HURLER'S SYNDROME
Authors: Danes B. Shannon , Bearn Alexander G.
Published: June 2004

Seven families affected with Hurler's syndrome have been studied using the methods of cell culture. Skin fibroblasts obtained from the skin of 7 patients with Hurler's syndrome contained metachromatic granules when stained for mucopolysaccharides with toluidine blue O and alcian blue, whereas fibroblasts from normal subjects contained no metachromatic granules.

In four families skin cultures of the clinically normal parents showed fibroblasts which contained demonstrable metachromatic granules and "gargoyle" cells and were considered to be heterozygous for the abnormal gene. Fibroblast cultures from certain other members of these families showed metachromasia. These findings were also considered to indicate heterozygosity for the abnormal gene.

Three families of the X-linked type of the disease were studied. Fibroblasts cultured from the father contained no metachromatic granules whereas those of the hemizygous mother contained both metachromatic granules and "gargoyle" cells. In one family the abnormal gene could be traced through unaffected individuals for three generations. The prolonged preservation of the biochemical trait in tissue culture will permit studies to be performed designed to clarify the primary action of the abnormal genes which result in Hurler's syndrome, as well as to increase the usefulness of this trait in mapping the human X chromosome.
THE FUNCTIONS OF THE THYMUS SYSTEM AND THE BURSA SYSTEM IN THE CHICKEN
Authors: Cooper Max D. , Peterson Raymond D. A. , South Mary Ann , Good Robert A.
Published: June 2004

The bursa of Fabricius and the thymus are "central lymphoid organs" in the chicken, essential to the ontogenetic development of adaptive immunity in that species. Surgical removal of one or both of these organs in the newly hatched chicken, followed by sublethal X-irradiation the next day, has permitted recognition of two morphologically distinct cell systems in the "peripheral lymphoid tissues" of the spleen, gut, and other organs, and clear definition of the separate functions of each cell system.

The thymus-dependent development is represented morphologically by the small lymphocytes of the circulation and the white pulp type of development in the tissues. As in mammals, the thymus-dependent tissues of the chicken are basic to the ontogenesis of cellular immunity: graft versus host reactions, responses of delayed hypersensitivity and homograft rejection; and play a less clearly defined role in the antibody response to at least some antigens. Thymectomized-irradiated chickens are deficient in all these responses, and grow more slowly than any of the other experimental groups. In these animals germinal centers, plasma cells, and capacity for immunoglobulin synthesis remain intact.

The bursa-dependent development is represented morphologically by the larger lymphocytes of the germinal centers and the plasma cells, and functionally by the immunoglobulins. Bursectomized-irradiated chickens are agammaglobulinemic and unable to produce detectable antibody despite intense, repeated stimulation with bovine serum albumin and Brucella abortus organisms. The thymus-dependent development in these animals seems to be normal; they have adequate numbers of lymphocytes in the circulation and tissues, are able to reject skin homografts, though more slowly than usual, and to exercise graft versus host reactions. The short life span of these chickens has precluded adequate study of responses of delayed hypersensitivity.

There was no evidence of significant impairment of reticuloendothelial function in either the bursectomized-irradiated or the thymectomized-irradiated group, as judged by the clearance of colloidal gold and I131-tagged keyhole limpet hemocyanin.
THE ROLE OF THE MICROBIAL FLORA IN UREMIA
Authors: Einheber Albert , Carter Darryl
Published: June 2004

Germfree rats were used in 3 experiments to study the effects of the microbial flora on survival time after acute uremia produced by a one-stage bilateral nephrectomy. Germfree rats, limited-flora rats, and conventionalized rats (all maintained continuously in isolators) were subjected to nephrectomy or to sham nephrectomy, deprived of food and water until they died, respectively, of uremia or of starvation, and their survival times compared. To establish a limited defined flora in advance of nephrectomy, germfree rats were either monocontaminated (Staphylococcus albus), dicontaminated (S. albus and Proteus mirabilis) or tetracontaminated (S. albus, S. faecalis, P. mirabilis, and E. coli); to conventionalize germfree rats, they were exposed to the mixed microbial flora contained in the cecal contents of ordinary rats, which was the source of the aforementioned bacteria and which included other uncharacterized microorganisms as well.

The intestine of all rats with a limited flora persisted in a morphologic state that was virtually no different from that of the germfree rat, including the presence of an enlarged, thin-walled cecum; by contrast, the intestine of the conventionalized rats permanently assumed the morphological characteristics of ordinary, open-laboratory rats with the cecum reduced to normal size.

After nephrectomy and food and water deprivation (death from anuria):

(a) All germfree rats but one outlived their conventionalized counterparts in each of the 3 experiments; the 21 germfree rats (127 hr) lived, on the average, 2 days longer than did the 24 conventionalized rats (75 hr). No sex difference was demonstrated.

(b) The rats with a limited flora died correspondingly sooner as the complexity of their flora increased; survival time of the tetracontaminated rats was significantly shorter than that of the germfree rats, and statistically no different from that of the conventionalized rats.

After sham nephrectomy and food and water deprivation (delayed death from starvation):

(a) All rats, irrespective of microbial status or sex, outlived their fasting nephrectomized partners. The conventionalized rats endured starvation approximately 2.5 wk longer than they did anuria and the germfree rats 1 wk longer.

(b) All conventionalized rats, both male and female, outlived their respective germfree counterparts by about 1 wk.

(c) All males, irrespective of microbial status, survived longer than did the females; the average difference was 4 days.

The differences in tolerance to anuria or starvation did not correlate with initial body weight or rate of weight loss.