bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Nontoxic Concentrations of Piperacillin/Tazobactam for Intravitreal Application
Authors: Özkiriş Abdullah , Evereklioglu Cem , Kontaş Olgun , Öztürk Öner Ayşe , Erkiliç Kuddusi 
Published: April 2004

<i>Background:</i> To investigate the highest nontoxic intravitreal dose of piperacillin/tazobactam in rabbits. <i>Material and Methods:</i> Forty New Zealand white albino rabbits were used in this study. The rabbits were divided into four equal groups (10 rabbits in each) and the right eyes were treated with 0.1 ml intravitreal injections of 1,000 µg piperacillin/tazobactam in group 1, 500 µg in group 2, 250 µg in group 3, and 100 µg in group 4. The left eyes served as controls and were injected with 0.1 ml of saline solution. Ganzfeld electroretinogram (ERG) was performed on all eyes before and after 4 weeks of intravitreal injections. Then, the rabbits were killed and the eyes were enucleated for histopathological evaluation of the retina. Retinal sections were evaluated by morphometric analyses on cell counts of ganglion cell layer and thickness of the various retinal layers. <i>Results:</i> Baseline ERGs were similar among the groups (p > 0.05). After 4 weeks of injection, there were a reduction of the b-wave amplitude and extension of the b-wave implicit time in photopic and scotopic ERGs in group 1 and group 2 when compared with controls (for each, p < 0.001). Intravitreal injection of 100 and 250 µg piperacillin/tazobactam did not cause any deterioration of the b-wave of ERGs throughout the follow-up period of 4 weeks (for each, p > 0.05). After morphometric analysis of retinal sections in all groups, there were no statistically significant differences in the mean number of surviving ganglion cells, thickness of the whole retina and the inner plexiform layer compared with controls (p > 0.05). <i>Conclusion:</i> 250 µg/0.1 ml piperacillin/tazobactam is the highest nontoxic dose to the normal retinas of adult albino rabbits as intravitreal injection. Piperacillin/tazobactam may be a new, potentially important drug in the treatment of endophthalmitis as it has a broad antimicrobial spectrum.
Corneal Concentrations following Systemic Administration of Amphotericin B and Its Lipid Preparations in a Rabbit Model
Authors: Goldblum David , Rohrer Kaspar , Frueh Beatrice E. , Theurillat Regula , Thormann Wolfgang , Zimmerli Stefan 
Published: April 2004

<i>Background:</i> Amphotericin B (AmB) and various lipid formulations of AmB are available for the treatment of fungal infections of the eye. Currently, the recommended route of administration for the treatment of fungal keratitis is by topical application. Nevertheless, because of the risk of a difficult to treat exogenous fungal endophthalmitis, a combined topical and systemic treatment is frequently given when treating deep fungal keratitis. To date, little is known about the pure corneal availability of these drugs following systemic treatment. In this study, the corneal concentration following 7 daily doses of parenteral AmB lipid complex (ABLC) or liposomal AmB (L-AmB) was compared to that of AmB deoxycholate (D-AmB) in a rabbit model. <i>Methods:</i> Following induction of uveitis in one rabbit eye by intravitreal injection of endotoxin, daily doses of D-AmB (1 mg/kg), ABLC (5 mg/kg) or L-AmB (5 mg/kg) were given intravenously on 7 consecutive days. Five or more rabbits per treatment were used. AmB concentrations were determined by high-performance liquid chromatography (HPLC) in corneas collected at autopsy 24 h after the 7th and final dose. Data were analyzed using the Mann-Whitney U test. <i>Results:</i> After 7 days of treatment, mean corneal concentrations of AmB in the inflamed eyes were significantly higher (2.38 ± 1.47 µg/g; p < 0.01) following treatment with L-AmB compared with ABLC (<0.1 µg/g) and D-AmB (0.46 ± 0.2 µg/g). No AmB could be detected in the corneas of the non-inflamed eyes. <i>Conclusion:</i> In our rabbit model, AmB penetration into the cornea was significantly higher after systemic administration of L-AmB compared with conventional D-AmB or ABLC.
Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators inBrachyhypopomus pinnicaudatusfrom a temperate climate
Authors: Quintana Laura , Silva Ana , Berois Nibia , Macadar Omar 
Published: April 2004

SUMMARYIn contrast to most of the previous studies in gymnotiform reproduction,which have been conducted in the tropical region, this study examines a gymnotid from the temperate region in both the natural habitat and the laboratory. The gonadal histology of Brachyhypopomus pinnicaudatus is described for the first time. The male had a paired, lobular testis of the unrestricted spermatogonial type, and females a paired saccular cystovary. Analysis of gonads and their annual cycle enabled us to confirm the breeding season and to conclude that this species is a multiple spawner. Water temperature and photoperiod showed the expected annual cycles for the region. High temperature and a 14 h:10 h L:D photoperiod in the natural habitat coincided with (1) mature gonadal stages, (2) electrophysiological sexual dimorphism: males present a lengthened negative phase in their electric organ discharge (EOD) and (3) decreased temperature sensitivity of the EOD: the waveform does not change when temperature increases above 20°C. Acclimation to sustained high temperature (30 days, 28°C, 12 h:12 h L:D,low conductivity) induced gonad maturation along with EOD dimorphism. Our data show that high environmental temperature is enough to trigger sexual maturity in Brachyhypopomus pinnicaudatus from a temperate climate.
Escape behavior and escape circuit activation in juvenile crayfish during prey–predator interactions
Authors: Herberholz Jens , Sen Marjorie M. , Edwards Donald H. 
Published: April 2004

SUMMARYThe neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey–predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all three known types of escape tail-flips during the interactions with the dragonfly nymphs. Tail-flips generated by activity in the giant neurons were predominantly observed to trigger the initial escape responses to an attack, but non-giant mediated tail-flips were often generated to attempt escape after capture. Attacks to the front of the crayfish triggered tail-flips mediated either by the medial giant neuron or by non-giant circuitry, whereas attacks to the rear always elicited tail-flips mediated by the lateral giant neuron. Overall, tail flipping was found to be a successful behavior in preventing predation, and only a small percentage of crayfish were killed and consumed.
Thermodynamics of organic compound transfer from the gas phase to environmentally important sorbents
Authors: Borisover Mikhail , Graber Ellen R. 
Published: April 2004

AbstractLinear Free Energy Relationships (LFERs) based on distribution coefficients between the aqueous phase and the sorbent are often unsuccessful for interpreting sorption mechanisms in environmentally important sorbents because they comprise contributions not only from solute interactions with the sorbent, but also from hydration of the solute in bulk water. To avoid this problem, we suggest an approach for studying interactions between organic sorbates and environmentally important sorbents using a thermodynamic cycle to eliminate interactions between the solute and bulk water. In this approach, aqueous distribution coefficients are converted to gas phase distribution coefficients that are related to the free energy of transfer from the gas phase to the hydrated sorbent, and include contributions from all interactions occurring during the transfer. Gas phase distribution coefficients are compared for different compounds with similar molar refraction values to give insights into the nature of specific and nonspecific interactions of organic molecules with environmental sorbents. This methodology is illustrated for sorption of organic molecules in soil organic carbon and at mineral surfaces, and examples of insights obtainable from this methodology are given.
Volatile organic compound emissions from terrestrial ecosystems: A primary biological control over atmospheric chemistry
Authors: Monson Russell K. 
Published: April 2004

AbstractPlants produce a variety of non‐methane volatile organic compounds (NMVOCs) that react with photochemical components of the atmosphere and influence the production of atmospheric oxidants. In this review, the case is made that biogenic NMVOC emissions exert one of the primary controls over regional and global atmospheric chemistry. The diversity of biogenic, reactive organic compounds capable of fueling atmospheric chemistry is immense, including terpenes, alcohols, aldehydes, ketones, and organic acids. Considerable effort has been devoted to the design of models capable of predicting NMVOC emission rates, and thus driving atmospheric chemistry models. Over the past decade, however, what once seemed like promising conceptual connections of NMVOC emissions to fundamental biochemical processes such as photosynthesis, have not been realized; this has delayed the development of mechanistic NMVOC emissions models. Future progress in this area will require new subcellular experimental systems, and the biochemical insight that will accompany these investigations. The past use of existing coupled biogenic emission—photochemistry models at the global scale, even with their mechanistic limitations, has revealed the potential for NMVOC emissions from terrestrial ecosystems to cause reductions in tropospheric hydroxyl radical concentration and increases in the concentration and lifetime of radiatively important trace gases such as methane and ozone.
Structure of self‐assembled monolayers of semifluorinated alkanethiols on gold and silver substrates
Authors: Frey S. , Heister K. , Zharnikov M. , Grunze M. , Tamada K. , Colorado R. , Graupe M. , Shmakova O. E. , Lee T. R. 
Published: April 2004

AbstractSelf‐assembled monolayers (SAMs) formed from semifluorinated alkanethiols (SFATs) CF3(CF2)9(CH2)nSH (F10HnSH: n = 2, 11, and 17) on poly‐crystalline Au and Ag were characterized by X‐ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and near edge X‐ray absorption fine structure spectroscopy. SFATs were found to form highly ordered and densely packed SAMs on both substrates. The molecules are strongly bonded to the substrates via their sulfur head groups, in the same manner as conventional alkanethiol (AT) SAMs. The hydrocarbon (except for n = 2) and fluorocarbon parts of the adsorbed SFATs retain the expected planar zigzag and helical conformations of the respective bulk materials. The orientation of the fluorocarbon chains does not depend on the substrate. These entities are almost perpendicular to the substrate in F10H2S/Au and F10H2S/Ag and become slightly more tilted in SFAT SAMs with longer hydrocarbon moieties. However, the alkyl parts of the SFAT films exhibit tilt and twist angles that are similar to those of normal alkanethiol films on Ag and Au substrates despite the reduced packing density in the SFAT films as compared to normal AT SAMs. We suggest that the substrate‐related differences in tilt and twist angles for both systems are associated with the different character of the head‐group‐substrate bonding on Au and Ag.
Detection of time‐resolved photoionization currents from pesticide‐contaminated vegetation
Authors: Kadosh Michal , Gridin Vladimir V. , Schechter Israel 
Published: April 2004

AbstractMultiphoton‐ionization fast‐conductance (MPI‐FC) was directly applied for detection of photoionization currents originated from pesticide traces irradiated by UV‐laser. The principal methodology required for direct screening of pesticide traces deposited on various vegetational specimens was addressed. This approach was exemplified with 1,2,3,4,5,6‐hexachlorocyclohexane and 3‐amino‐1,2,4‐triazole, which are frequently found in agriculture‐related industries. The range of pesticide concentrations covered was from 0.001 ng/mL to 1 mg/mL, and all measurements were carried out under ambient conditions. Our target vegetation substrates were sampled from the outdoors: grass, plant, and/or tree leaves. Neither material purification nor laborious extraction routines were utilized; thus employing MPI‐FC for in situ/on‐line monitoring of pesticide‐contaminated vegetation is feasible.
Synthesis, characterization, and magnetic properties of α‐MnS nanocrystals
Authors: Kan Shihai , Felner Israel , Banin Uri 
Published: April 2004

AbstractMnS nanocrystals have been prepared by a colloidal synthesis route through the reaction of MnCl2 and S[Si(CH3)3]2 in trioctylphosphineoxide. The nanocrystals were characterized using X‐ray diffraction and transmission electron microscopy. The magnetic properties were studied with SQUID magnetometry. X‐ray diffraction shows that the nanocrystals are of the thermodynamically stable α‐MnS (alabandite) structure. Size control was achieved by changing the concentration of the precursors. Nanocrystal sizes were measured by transmission electron microscopy, and three samples of average diameters 20, 40, and 80 nm were obtained, with narrow size distribution (σ˜9%). The zero field cooled magnetization curves for the 80‐, 40‐, and 20‐nm samples showed a cusp at 116 K, 97 K, and 50 K respectively, all smaller than the antiferromagnetic transition temperature, TN = 130 K, of bulk α‐MnS. Below TN the magnetization exhibits a paramagnetic behavior unlike typical antiferromagnetic materials. These results indicate that there is a mixture of paramagnetic and antiferromagnetic phases in the nanocrystals. The size dependence shows a general trend of decrease of TN with reduced particle size, indicating size dependent magnetic ordering.
Quantum‐mechanical reaction rate constants from centroid molecular dynamics simulations: Barrier crossing in an asymmetrical double‐well
Authors: Navrotskaya Irina , Shi Qiang , Geva Eitan 
Published: April 2004

AbstractQuantum‐mechanical reaction rate constants were calculated from centroid molecular dynamics (CMD) simulations, for the case of barrier crossing in an asymmetrical double‐well potential bilinearly coupled to a harmonic bath. The calculation is based on a recently proposed formulation of the reaction rate constant in terms of the position—flux correlation function, which can be approximated via CMD in a well‐defined manner. The predictions of CMD and various simplified versions of it are compared to exact results, which were obtained via the quasi‐adiabatic propagator path integral (QUAPI) method, and/or path integral quantum transition state theory (PI‐QTST). The predictions based on CMD are found to be in good agreement with both.
Semiconductor nanorods: Cu, Zn, and Cd chalcogenides
Authors: Govindaraj A. , Leonard Deepak F. , Gunari N. A. , Rao C.N.R. 
Published: April 2004

AbstractSemiconductor nanorods have been synthesized by the use of surfactants. The nanorods of CuS, ZnS, CdS, CuSe, ZnSe, and CdSe have diameters in the 5–150 nm range and exhibit high aspect ratios, with lengths of up to several microns. By using a high surfactant concentration, nanotube‐like structures of CdS and CdSe with high aspect ratios are obtained. All the chalcogenide nanostructures possess hexagonal structures, independent of the structures of the stable phases of the materials.
Self‐assembled monolayers of metallosalophenes on gold
Authors: Beulen Marcel W. J. , Van Veggel Frank C. J. M. , Reinhoudt David N. 
Published: April 2004

AbstractSalophene complexes of transition metals exhibit a reversible electrochemistry. We have synthesized salophene complexes with sulfur‐containing sub‐stituents aimed at the formation of self‐assembled monolayers on a gold surface. Such monolayers have interesting cation complexating properties. The monolayers were fully characterized by wettability studies, grazing‐angle Fourier transform infrared spectroscopy (FT‐IRS), X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS), and electrochemical capacitance measurements. These measurements indicate liquid‐like monolayers. Cation complexation could be monitored indirectly by electrochemical impedance spectroscopy measurements, showing responses for Na+ and K+. This complexation behavior of the metallosalophene monolayers could not be studied directly by electrochemistry of the metallosalophene either due to electrochemical instability of the monolayer or a smeared redox response.
Polystyrene‐Supported 2‐Arylindenyl Zirconocene Catalysts for Propylene Polymerization
Authors: Diehl Stephen C. , Waymouth Robert M. 
Published: April 2004

AbstractMono‐ and bis 2‐arylindenyl zirconocene/methylalumoxane (MAO) catalysts are prepared on a crosslinked polystyrene resin using gel‐phase organic reactions. The 2‐arylindene ligands are bonded to the polystyrene backbone through a disiloxane linkage, and the zirconocene is prepared directly on the support in high yield. These supported 2‐arylindenylzirconocenes in the presence of MAO show high activity and yield polypropylenes with microstructures similar to those produced by the analogous solution‐phase catalysts.
A mild route to α‐alkoxyacetylenes mediated by lewis acids and synthetic routes to 10‐, 11‐, and 12‐membered ring enediyne carbocycles
Authors: Comanita Bogdan M. , Heuft Matthew A. , Rietveld Tanya , Fallis Alex G. 
Published: April 2004

AbstractThe condensation of silyl substituted acetylenes with dimethoxy acetals via a modified “Mukaiyama‐type reaction” to afford α‐alkoxyacetylenes is described. These propargylic ethers 17–21 were synthesized from the reaction of aluminum or zinc acetylides with acetals mediated by Lewis acids. In appropriate cases, when a second acetal was present in the initial acyclic product (24), a subsequent intramolecular acetal‐ene (Prins) cyclization ensued to afford the silylalkylidenealkoxycyclopentane (25). Enediyne species were unreactive under these conditions, even in an intramolecular case. Routes to 11‐ and 12‐membered carbocyclic enediyne compounds (43, 44) were developed via an intramolecular pinacol coupling of the dialdehydes 39 with sammarium diodide/HMPA. The requisite double bond was introduced using the thiocarbonate expulsion method with trimethyl phosphite. A route to the highly substituted 10‐membered ring enediyne 50 is also described based on the use of an isopropylidene acetal tether control group to facilitate an intramolecular chromium (II)/nickel (II)‐mediated coupling of the iodoacetylene aldehyde 49.
Thermal resonant tunneling rates by a generalized flux averaging method
Authors: Caspary Maytal , Berman Lihu , Peskin Uri 
Published: April 2004

AbstractThe calculation of the thermal rate constant as a time integral over flux‐flux correlation functions is a challenging task when the potential energy along the reaction coordinate cannot be associated with a distinctive single barrier. In the case of resonant tunneling through a double barrier potential, the calculations may become formidable due to the population of long‐lived resonance states and the corresponding long time‐decay of the flux‐flux correlation functions. The flux averaging method was introduced recently in order to circumvent this problem in cases where the long time dynamics is due to a single resonance state with the longest lifetime in the system. In this work we generalize the method for calculations of thermal resonant‐tunneling rates in systems of many resonances, where the long time‐decay is accompanied by an internal dynamics within the quasi‐bound system. This extra complication is handled by additional averaging of flux‐flux correlation funcation over the time period of the internal dynamics. The result is an exact expression for the rate constant in terms of a linear combination of time integrals over flux‐flux correlation functions, which reaches its asymptotic time limit in a short (direct scattering) time, regardless of the long time‐decay of the flux‐flux correlation functions. This is derived for an analytic model system, and demonstrated in a numerical simulation of resonant tunneling through a double barrier potential.
Constraints on the glacial operation of the atlantic ocean's conveyor circulation
Authors: Broecker Wallace S. 
Published: April 2004

AbstractCirculation in the Atlantic Ocean is currently dominated by a northward flow of upper waters balanced by a return flow of deep water (i.e., the conveyor). Paleoproxies tell us that, unlike today, during the glacial age the deep Atlantic was stratified. Rather than being flooded with one nearly homogeneous water mass, there were two distinctly different ones. In this paper, the paleoproxy results are analyzed in an attempt to constrain the sources and ventilation rate of the deeper of these two glacial Atlantic water masses. Taken together, the cadmium and carbon isotope measurements on benthic foraminifera and the radiocarbon measurements on coexisting benthic and planktonic foraminifera appear to require a conveyor‐like circulation no weaker than half of today's. This conclusion is at odds with geostrophic reconstructions. This seeming disagreement could be eliminated if, as suggested by Keigwin and Schlegel, the radiocarbon measurements by Broecker et al. significantly underestimate the difference between the 14C to C ratio for glacialage surface water and deep water in the equatorial Atlantic.
Dealing with Uncertainty in Diffusion Tensor MR Data
Authors: Basser Peter J. , Pajevic Sinisa 
Published: April 2004

AbstractThis paper explains how radio frequency (RF) background noise produces uncertainty in measured diffusion tensor MRI (DT‐MRI) data, how this noise can be modeled, and how its effects can be mitigated. DT‐MRI data are derived from a series of magnitude diffusion‐weighted images (DWI) in which RF noise is rectified. A new Gaussian distribution is proposed that describes the variability of the estimated diffusion tensor,D, in an ideal experiment in which RF noise is the only artifact present. We show how to improve the design of DT‐MRI experiments by requiring that the statistical distribution ofDbe independent of the laboratory coordinate system. Non‐parametric empirical methods of analyzing uncertainty in DT‐MRI experiments are also described. Monte Carlo simulations are useful in designing and interpreting DT‐MRI experiments. Bootstrap methods help us measure the true variability ofD(and quantities derived from it), and assess the quality of DT‐MRI data. Matrix Perturbation techniques predict how the uncertainty inDpropagates to its eigenvalues and eigenvectors. A method for obtaining a continuous diffusion tensor field from the measured discrete noisy DT‐MRI data also reduces the uncertainty ofDand quantities derived from it. Finally, we describe schemes that use wavelets to remove noise from DWI and DT‐MRI data while preserving boundaries between different tissue regions. Collectively, these parametric and nonparametric methods provide a unified statistical framework to improve the design of DT‐MRI experiments and their subsequent analysis.