bluuebunny/crossref_metadata_2025 huggingface dataset:
Mapping basin scale variable source areas from multitemporal remotely sensed observations of soil moisture behavior
Authors: Verhoest Niko E. C. , Troch Peter A. , Paniconi Claudio , De Troch François P.
Published: February 2004

Soil moisture is an important and highly variable component of the hydrologic cycle. Active microwave remote sensing offers the potential for frequent observation of soil moisture at basin and regional scales. Notwithstanding recent advances, the goal of obtaining accurate and reliable measurements or maps of soil moisture from these instruments remains elusive. The main difficulties for active sensors such as synthetic aperture radar (SAR) are the combined effects of soil moisture, surface roughness, and vegetation on the backscattered signal. We show that it is possible to separate soil moisture information from the other physical factors that dominate the radar backscattering, such as topography and land cover, through a principal component analysis of a time series of eight European Remote Sensing (ERS) SAR images. The soil moisture patterns observed in one of the principal components are consistent with the rainfall‐runoff dynamics of a catchment and reflect the variable source areas occuring in the vicinity of the river network.
The discharge of nitrate‐contaminated groundwater from developed shoreline to marsh‐fringed estuary
Authors: Portnoy J. W. , Nowicki B. L. , Roman C. T. , Urish D. W.
Published: February 2004

As residential development, on‐site wastewater disposal, and groundwater contamination increase in the coastal zone, assessment of nutrient removal by soil and sedimentary processes becomes increasingly important. Nitrogen removal efficiency depends largely on the specific flow paths taken by groundwater as it discharges into nitrogen‐limited estuarine waters. Shoreline salinity surveys, hydraulic studies, and thermal infrared imagery indicated that groundwater discharge into the Nauset Marsh estuary (Eastham, Massachusetts) occurred in high‐velocity seeps immediately seaward of the upland‐fringing salt marsh. Discharge was highly variable spatially and occurred through permeable, sandy sediments during low tide. Seepage chamber monitoring showed that dissolved inorganic nitrogen (principally nitrate) traversed nearly conservatively from the aquifer through shallow estuarine sediments to coastal waters at flux rates of 1–3 mmol m−2 h−1. A significant relationship between pore water NO3‐N concentrations and NO3‐N flux rates may provide a rapid method of estimating nitrogen loading from groundwater to the water column.
Flow in rock fractures: The local cubic law assumption reexamined
Authors: Oron Assaf P. , Berkowitz Brian
Published: February 2004

We investigate the validity of applying the “local cubic law” (LCL) to flow in a fracture bounded by impermeable rock surfaces. A two‐dimensional order‐of‐magnitude analysis of the Navier‐Stokes equations yields three conditions for the applicability of LCL flow, as a leading‐order approximation in a local fracture segment with parallel or nonparallel walls. These conditions demonstrate that the “cubic law” aperture should not be measured on a point‐by‐point basis but rather as an average over a certain length. Extending to the third dimension, in addition to defining apertures over segment lengths, we find that the geometry of the contact regions influences flow paths more significantly than might be expected from consideration of only the nominal area fraction of these contacts. Moreover, this latter effect is enhanced by the presence of non‐LCL regions around these contacts. While contact ratios of 0.1–0.2 are usually assumed to have a negligible effect, our calculations suggest that contact ratios as low as 0.03–0.05 can be significant. Analysis of computer‐generated fractures with self‐affine walls demonstrates a nonlinear increase in contact area and a faster‐than‐cubic decrease in the overall hydraulic conductivity, with decreasing fracture aperture; these results are in accordance with existing experimental data on flow in fractures. Finally, our analysis of fractures with self‐affine walls indicates that the aperture distribution is not lognormal or gamma as is frequently assumed but rather truncated‐normal initially and increasingly skewed with fracture closure.
Source water assessment and nonpoint sources of acutely toxic contaminants: A review of research related to survival and transport ofCryptosporidium parvum
Authors: Walker Mark J. , Montemagno Carlo D. , Jenkins Michael B.
Published: February 2004

Amendments to the Safe Drinking Water Act (PL‐930123) in 1996 required that public water supply managers identify potential sources of contamination within contributing areas. Nonpoint sources of acutely toxic microbial contaminants, such asCryptosporidium parvum, challenge current approaches to source identification and management as a first step toward developing management plans for public water supply protection. Little may be known about survival and transport in the field environment, prescribed practices may not be designed to manage such substances, and infective stages may be present in vast numbers and may resist water treatment and disinfection processes. This review summarizes research related to survival and transport ofC.parvumoocysts, as an example of an acutely toxic contaminant with nonpoint sources in animal agriculture. It discusses ∥1) significance of infected domesticated animals as potential sources ofC. parvum, (2) laboratory and field studies of survival and transport, and (3) approaches to source control in the context of public health protection.
Irrivol: A method to estimate the yearly and monthly water applied in an irrigation district
Authors: Casterad M. A. , Herrero J.
Published: February 2004

Management of irrigation water requires knowledge of the volume of water that will be needed in each irrigated district. We present Irrivol, a method for estimation of irrigation water volumes that combines (1) the crop hectarages obtained either by area frame sampling or by a regression estimator with satellite data, and (2) the net crop water requirements (m3 ha−1) calculated by Food and Agriculture Organization (FAO) methodology. We also assess the sensitivity of the yearly and monthly estimates obtained by the use of either actual or of average meteorological data. The net crop water requirements (hm3) in the irrigation district of Flumen (Aragón, Spain) in 1991, 1993, and 1994 were estimated. The annual and monthly estimates were compared to the corresponding irrigation water volumes invoiced to farmers by the water authority. The most reliable irrigation water estimates were obtained by combining the crop hectarages calculated by the regression estimator with the weather of the actual year. The ratio of the invoiced water volumes and our estimates using the above method ranged from 1.08 to 1.21 for annual estimates and from 1.05 to 1.35 for most of the monthly estimates.
Irregular bed forms in steep, rough channels: 2. Field observations
Authors: Furbish David Jon , Thorne Stephen D. , Byrd Tracy C. , Warburton Jeff , Cudney Joseph J. , Handel Robert W.
Published: February 2004

A linear stability analysis using a flow model appropriate for steep, rough channels suggests that initial wavelength selection of alternate bars is strong for extant flow conditions in North Boulder Creek, Colorado. This is due in part to effects of velocity correlation terms in the streamwise momentum balance that involve deviations in velocity components about depth‐averaged values. The analysis also suggests that alternate bars and midchannel bars can “compete” during initial bed form growth at low sediment transport rates. These points are consistent with the observation that alternate and midchannel bar forms in North Boulder Creek have comparable topographic relief, as revealed by spectral analysis of the bed topography. Moreover, the dominant wavelengths of these bar forms match the fastest growing wavelengths predicted by the stability analysis. However, whereas the alternate bar topography can be attributed to free‐bar growth, much of the midchannel bar topography probably is a forced‐bar topography that is related to flow accelerations associated with variations in channel width. The complex bed topography of North Boulder Creek thus consists of a decipherable mixture of bed forms that have evolved as free alternate bars together with forced bars whose positions and geometries are fixed in relation to variations in channel width or to large immobile boulders.
Transient Dupuit Interface Flow with partially penetrating features
Authors: Bakker Mark
Published: February 2004

A comprehensive potential is presented for Dupuit interface flow in coastal aquifers where both the fresh water and salt water are moving. The resulting potential flow problem may be solved, for incompressible confined aquifers, using analytic functions. The vertical velocity of the interface may then be computed analytically and the change of the position of the interface may be simulated by numerical integration through time, starting with a known (or estimated) initial position. The upconing of the interface below a partially penetrating ditch or well may be studied if Dupuit solutions for such features are available. A new Dupuit solution is derived for a ditch that penetrates the aquifer partially from above; a Dupuit solution for a partially penetrating well may be obtained following a similar derivation. The new Dupuit solution is combined with the interface solution to simulate the upconing of an initially horizontal interface below a series of partially penetrating ditches; the interface converges to the known steady state position.
Influence of iron oxide inclusion shape on CoII/IIIEDTA reactive transport through spatially heterogeneous sediment
Authors: Szecsody James E. , Chilakapati Ashok , Zachara John M. , Garvin Amanda L.
Published: February 2004

Multisolute reactive transport was investigated in chemically heterogeneous systems to determine the influence of the shapes of the reactive heterogeneities (iron oxide inclusions) by comparison of two‐dimensional heterogeneous experiments with spatially averaged models that had differing inclusion characterization. Eleven reactions were considered in this system, starting with adsorption of the initial solute (CoIIEDTA) to Fe oxides, followed by two competing surface reactions: oxidation forming CoIIIEDTA and Fe dissolution forming FeIIIEDTA and Co2+. Spatial moments of the eight mobile species were compared between data and models. One spatially averaged model (homogeneous equivalent), which incorporated inclusion mass only, significantly under predicted oxidation (up to 74%), the influence of reaction kinetics, and species retardation. In contrast, the ensemble average model (incorporating inclusion mass and length) well predicted speciation, retardation, and skewness. This large difference in prediction between two spatially averaging models was caused by the lack of incorporation of contact time of solutes with iron oxides in the homogeneous equivalent model and the importance of the contact time with the differing timescales of reactions. Experimental and modeling results also showed that the uncertainty in prediction of specific species increased as the inclusions varied from more ideal (fixed‐length) to more natural (variable‐length) shape of inclusions.
Peak flow responses to clear‐cutting and roads in small and large basins, Western Cascades, Oregon: A second opinion
Authors: Thomas Robert B. , Megahan Walter F.
Published: February 2004

In this paper, we conduct a reanalysis of methods and data used by Jones and Grant [1996]. Data from three small watersheds (60–101 ha) and three pairs of large basins (60–600 km2) in Oregon's western Cascades were used to evaluate effects of timber harvest and road construction on peak flows. We could not detect any effect of cutting on peak flows in one of the large basin pairs, and results were inconclusive in the other two large basin pairs. One small watershed was 100% clear‐cut, a second was 31% patch‐cut with 6% of the area affected by road construction, and a third was held as a long‐term control. Peak flows were increased up to 90% for the smallest peak events on the clear‐cut watershed and up to 40% for the smallest peak flows on the patch‐cut and roaded watershed. Percentage treatment effects decreased as flow event size increased and were not detectable for flows with 2‐year return intervals or greater on either treated watershed. Treatment effects decreased over time but were still found after 20 years on the clear‐cut watershed but for only 10 years on the patch‐cut and roaded watershed.
Climatic and physical factors that influence the homogeneity of regional floods in southeastern Australia
Authors: Bates Bryson C. , Rahman Ataur , Mein Russell G. , Weinmann P. Erwin
Published: February 2004

The identification of hydrologically “homogeneous” regions is a primary step in many regional flood frequency techniques. Although statistical procedures for identifying homogeneous regions abound in the literature, there has been relatively little effort directed toward the identification of the physical and climatic basin characteristics that cause similarity in standardized flood peak distributions. We use regional flood peak and basin characteristics data for 104 basins in southeastern Australia to investigate the physical and climatic factors associated with the statistical distributions of flood peaks; the degree of geographical coherence of homogeneous regions; and the extent to which information on flood peak statistics is encapsulated by the physical and climatic characteristics of basins that are commonly used in regionalization studies. Our results show that (1) membership of a particular homogeneous region is determined largely by a combination of climatic characteristics that is related to runoff generation; (2) supergroups consisting of sites within aggregated homogeneous regions that have reasonably similar flood responses show some degree of spatial coherence; and (3) the basin characteristics that influence regional homogeneity can be identified despite the use of indices that smooth spatial and temporal variability.
Air sparging: Air‐water mass transfer coefficients
Authors: Braida Washington J. , Ong Say Kee
Published: February 2004

Experiments investigating the mass transfer of several dissolved volatile organic compounds (VOCs) across the air‐water interface were conducted using a single‐air‐ channel air‐sparging system. Three different porous media were used in the study. Air velocities ranged from 0.2 cm s−1 to 2.5 cm s−1. The tortuosity factor for each porous medium and the air‐water mass transfer coefficients were estimated by fitting experimental data to a one‐dimensional diffusion model. The estimated mass transfer coefficients KG ranged from 1.79 × 10−3 cm min−1 to 3.85 × 10−2 cm min−1. The estimated lumped gas phase mass transfer coefficients KGa were found to be directly related to the air diffusivity of the VOC, air velocity, and particle size, and inversely related to the Henry's law constant of the VOCs. Of the four parameters investigated, the parameter that controlled or had a dominant effect on the lumped gas phase mass transfer coefficient was the air diffusivity of the VOC. Two empirical models were developed by correlating the Damkohler and the modified air phase Sherwood numbers with the air phase Peclet number, Henry's law constant, and the reduced mean particle size of porous media. The correlation developed in this study may be used to obtain better predictions of mass transfer fluxes for field conditions.
Mixing and stretching efficiency in steady and unsteady groundwater flows
Authors: Weeks Scott W. , Sposito Garrison
Published: February 2004

Mixing is the physical process through which solute is spread into a fluid by the stretching and folding of material lines and surfaces. Mixing, as compared to dilution, is important to solute spreading by groundwater because it operates on much shorter timescales than does dilution, and it provides the increased plume boundary area and high local concentration gradients that promote effective solute dilution. In this paper, the mixing process is investigated theoretically for subsurface tracer plume movement, using as heuristic examples both steady and unsteady groundwater flows in a perfectly stratified aquifer whose properties mimic those of the sand aquifer at the Borden site. It is shown that the stretching efficiency, a parameter that characterizes the effectiveness of mixing, is largest at transitions between regions of highly contrasting hydraulic conductivity and, more broadly, that pronounced spatial variability in the hydraulic conductivity is conducive to good mixing because of the periodic resurgences in material line stretching that it causes. Unsteady groundwater flow resulting from a decrease in vertical groundwater flux with time leads to greater rates of material line stretching than do steady flows, whereas little difference from the steady flow case occurs for unsteady groundwater flow under a time‐varying horizontal hydraulic head gradient. Overall, pronounced spatial variability in the hydraulic conductivity is the most important contributor to good mixing of a tracer solute plume, but highly effective mixing requires additional physical conditions that induce chaotic solute pathlines.
Simulation of groundwater age distributions
Authors: Varni Marcelo , Carrera Jesús
Published: February 2004

The objective of our work is to examine how to simulate the age of groundwater in such a way that it can be compared to actual measurements. We start by showing that computation of kinematic age, the one obtained by tracking water along streamlines, is ill posed in heterogeneous aquifers. This, together with its inability to account for mixing processes, makes it inadequate for comparison with age measurements, which are the result of some averaging of the age distribution in the water sample (the type of averaging depends on the measurement procedure). Therefore we go on to write the equations for the cumulative distribution function of residence time under transient flow conditions. This allows us to derive transient equations for the mean age, as well as for the higher‐order moments of its distribution, which generalize previous results by others. These moments can be used for approximating age measurements, which need not be equal to the mean age of the water sample. Using both a synthetic and a real example, we show that mean age is an acceptable estimate of radiometric age measurements in many cases. Including a second‐order correction (variance of residence time distribution) always improves results. On the other hand, higher‐order approximations converge slowly for old (compared to half‐life) waters, to the point that third‐order approximations often worsen the results.
Primary infantile glaucoma in an Australian population
Authors: MacKinnon Jane R , Giubilato Antonio , Elder James E , Craig Jamie E , Mackey David A
Published: February 2004

Background: Primary infantile glaucoma presents rarely, but can be responsible for significant visual morbidity. There is little information on the clinical features and visual outcome of a pure population of primary infantile glaucoma, as opposed to a mixed population of primary and secondary glaucoma or combined group of those with trabeculodysgenesis and iridotrabeculodysgenesis.

Methods: We conducted a retrospective review of children with primary infantile glaucoma seen in south‐eastern Australia between 1980 and 2000, using The Royal Children's Hospital ophthalmic diagnostic coding database.

Results: Fifty‐one patients with primary infantile glaucoma were identified (83 eyes). This equates to an estimated incidence of approximately 1 in 30 000 births. The mean ± SD age at presentation was 135 ± 84 days. ‘Burnt‐out’ disease (megalocornea without raised intraocular pressure) was diagnosed in 10.8%. Goniotomy was the most commonly performed surgical procedure (69.4% of 72 eyes). Surgical success with one or two goniotomies was achieved in 74% of eyes. Visual outcomes at final review were generally good with 61.8% reading 6/12 or better. There were a disproportionately high number of children having a final recorded acuity of <6/60 in the group diagnosed in the first 3 months of life.

Conclusions: Primary infantile glaucoma is a rare ocular condition in this population that presents at a mean age of 4.4 months. Surgical and visual outcomes are generally favourable.
Clinical Case Notes
Authors: Colley Stephen M , Elston John S
Published: February 2004

A 68‐year‐old woman with metastatic breast cancer presented with slowly progressive visual loss in each eye. Electrophysiology confirmed bilateral optic neuropathies. Investigations to determine the cause of the vision loss were negative. Cessation of tamoxifen resulted in a dramatic improvement in acuity.
Clinical Case Notes
Authors: Kleinschmidt Andrew , Sullivan Timothy J , Mitchell Ken
Published: February 2004

Angiographically documented aneurysms of the intraorbital ophthalmic artery are extremely rare. Two cases are presented of intra­orbital ophthalmic artery aneurysms, both associated with arteriovenous malformation (AVM). There have only been isolated reports documenting this combination of vascular anomalies. In the first case, the aneurysm was treated conservatively and in the second case, after staging angiography and interventional embolization, the aneurysm was removed along with the associated AVM. The clinical presentation, pathogenesis and management of this rare combination of vascular anomalies is briefly discussed.
Oxidation of 4‐hydroxy‐2‐nonenal by succinic semialdehyde dehydrogenase (ALDH5A)
Authors: Murphy Tonya C. , Amarnath Venkataraman , Gibson K. Michael , Picklo Sr Matthew J.
Published: February 2004

Elevated levels of 4‐hydroxy‐trans‐2‐nonenal (HNE) are implicated in the pathogenesis of numerous neurodegenerative disorders. Although well‐characterized in the periphery, the mechanisms of detoxification of HNE in the CNS are unclear. HNE is oxidized to a non‐toxic metabolite in the rat cerebral cortex by mitochondrial aldehyde dehydrogenases (ALDHs). Two possible ALDH enzymes which might oxidize HNE in CNS mitochondria are ALDH2 and succinic semialdehyde dehydrogenase (SSADH/ALDH5A). It was previously established that hepatic ALDH2 can oxidize HNE. In this work, we tested the hypothesis that SSADH oxidizes HNE. SSADH is critical in the detoxification of the GABA metabolite, succinic semialdehyde (SSA). Recombinant rat SSADH oxidized HNE and other α,β‐unsaturated aldehydes. Inhibition and competition studies in rat brain mitochondria showed that SSADH was the predominant oxidizing enzyme for HNE but only contributed a portion of the total oxidizing activity in liver mitochondria. In vivo administration of diethyldithiocarbamate (DEDC) effectively inhibited (86%) ALDH2 activity but not HNE oxidation in liver mitochondria. The data suggest that a relationship between the detoxification of SSA and the neurotoxic aldehyde HNE exists in the CNS. Furthermore, these studies show that multiple hepatic aldehyde dehydrogenases are able to oxidize HNE.
Proteasomal inhibition causes the formation of protein aggregates containing a wide range of proteins, including nitrated proteins
Authors: Hyun Dong‐Hoon , Lee MoonHee , Halliwell Barry , Jenner Peter
Published: February 2004

Mutations in Cu,Zn‐superoxide dismutase (SOD‐1) are associated with some familial cases of amyotrophic lateral sclerosis (ALS), but it is not known how they result in cell death. We examined effects of overexpression of wild‐type SOD‐1 or the G37R or G85R mutations on the accumulation of ubiquitinated and nitrated proteins, and on loss of cell viability induced by the proteasome inhibitor, lactacystin. Wild‐type SOD‐1 had no effect on proteasomal activity, but the mutants decreased it somewhat. Treatment with lactacystin (1 µm) caused only limited cell viability loss, even though it induced a marked inhibition of proteasomal activities. However, viability loss due to apoptosis was substantial in response to lactacystin when cells were overexpressing a mutant SOD‐1. The frequency of cells showing immunoreactivity against ubiquitinated‐ or nitrated‐proteins was enhanced when wild‐type and mutant SOD‐1 s were overexpressed. Ubiquitinated or nitrated α‐tubulin, SOD‐1, α‐synuclein and 68K neurofilaments were observed in the aggregates. Similar aggregates were observed in cells overexpressing mutant parkin (Del3–5, T240R and Q311′X). The nitric oxide synthase inhibitor,l‐NAME, decreased viability loss and aggregation, suggesting that nitration of proteins may play an important role in aggregation and in the cell death accompanying it.
Prevention of NMDA‐induced death of cortical neurons by inhibition of protein kinase Cζ
Authors: Koponen Susanna , Kurkinen Kaisa , Åkerman Karl E. O. , Rosen Daria Mochly , Chan Pak H. , Koistinaho Jari
Published: February 2004

Excitotoxicity through stimulation of N‐methyl‐d‐aspartate (NMDA) receptors contributes to neuronal death in brain injuries, including stroke. Several lines of evidence suggest a role for protein kinase C (PKC) isoforms in NMDA excitotoxicity. We have used specific peptide inhibitors of classical PKCs (α, β, and γ), novel PKCs δ and ε, and an atypical PKCζ in order to delineate which subspecies are involved in NMDA‐induced cell death. Neuronal cell cultures were prepared from 15‐day‐old mouse embryos and plated onto the astrocytic monolayer. After 2 weeks in vitro the neurons were exposed to 100 µm NMDA for 5 min, and 24 h later the cell viability was examined by measuring the lactate dehydrogenase release and bis‐benzimide staining. While inhibitors directed to classical (α, β, and γ) or novel PKCs (δ or ε) had no effect, the PKCζ inhibitor completely prevented the NMDA‐induced necrotic neuronal death. Confocal microscopy confirmed that NMDA induced PKCζ translocation, which was blocked by the PKCζ inhibitor. The NMDA‐induced changes in intracellular free Ca2+ were not affected by the peptides. In situ hybridization experiments demonstrated that PKCζ mRNA is induced in the cortex after focal brain ischemia. Altogether, the results indicate that PKCζ activation is a downstream signal in NMDA‐induced death of cortical neurons.
Opposite regulation by typical and atypical anti‐psychotics of ERK1/2, CREB and Elk‐1 phosphorylation in mouse dorsal striatum
Authors: Pozzi Laura , Håkansson Kerstin , Usiello Alessandro , Borgkvist Anders , Lindskog Maria , Greengard Paul , Fisone Gilberto
Published: February 2004

The two mitogen‐activated protein kinases (MAPKs), extracellular signal‐regulated protein kinase 1 and 2 (ERK1/2), are involved in the control of gene expression via phosphorylation and activation of the transcription factors cyclic AMP response element binding protein (CREB) and Elk‐1. Here, we have examined the effect of haloperidol and clozapine, two anti‐psychotic drugs, and eticlopride, a selective dopamine D2 receptor antagonist, on the state of phosphorylation of ERK1/2, CREB and Elk‐1, in the mouse dorsal striatum. Administration of the typical anti‐psychotic haloperidol stimulated the phosphorylation of ERK1/2, CREB and Elk‐1. Virtually identical results were obtained using eticlopride. In contrast, the atypical anti‐psychotic clozapine reduced ERK1/2, CREB and Elk‐1 phosphorylation. This opposite regulation was specifically exerted by haloperidol and clozapine on ERK, CREB, and Elk‐1 phosphorylation, as both anti‐psychotic drugs increased the phosphorylation of the dopamine‐ and cyclic AMP‐regulated phosphoprotein of 32 kDa (DARPP‐32) at the cyclic AMP‐dependent protein kinase (PKA) site. The activation of CREB and Elk‐1 induced by haloperidol appeared to be achieved via different signalling pathways, as inhibition of ERK1/2 activation abolished the stimulation of Elk‐1 phosphorylation without affecting CREB phosphorylation. This study shows that haloperidol and clozapine induce distinct patterns of phosphorylation in the dorsal striatum. The results provide a novel biochemical paradigm elucidating the molecular mechanisms underlying the distinct therapeutic actions of typical and atypical anti‐psychotic agents.
Angiotensin AT4 ligands are potent, competitive inhibitors of insulin regulated aminopeptidase (IRAP)
Authors: Lew Rebecca A. , Mustafa Tomris , Ye Siying , McDowall Sharon G. , Chai Siew Yeen , Albiston Anthony L.
Published: February 2004

Angiotensin IV (Ang IV) exerts profound effects on memory and learning, a phenomenon ascribed to its binding to a specific AT4 receptor. However the AT4 receptor has recently been identified as the insulin‐regulated aminopeptidase (IRAP). In this study, we demonstrate that AT4 receptor ligands, including Ang IV, Nle1‐Ang IV, divalinal‐Ang IV, and the structurally unrelated LVV‐hemorphin‐7, are all potent inhibitors of IRAP catalytic activity, as assessed by cleavage of leu‐β‐naphthylamide by recombinant human IRAP. Both Ang IV and divalinal–Ang IV display competitive kinetics, indicating that AT4 ligands mediate their effects by binding to the catalytic site of IRAP. The AT4 ligands also displaced [125I]‐Nle1‐Ang IV or [125I]‐divalinal1‐Ang IV from IRAP‐HEK293T membranes with high affinity, which was up to 200‐fold greater than in the catalytic assay; this difference was not consistent among the peptides, and could not be ascribed to ligand degradation. Although some AT4 ligands were subject to minor cleavage by HEK293T membranes, none were substrates for IRAP. Of a range of peptides tested, only vasopressin, oxytocin, and met‐enkephalin were rapidly cleaved by IRAP. We propose that the physiological effects of AT4 ligands result, in part, from inhibition of IRAP cleavage of neuropeptides involved in memory processing.
Estrogen‐dependent alterations in D2/D3‐induced G protein activation in cocaine‐sensitized female rats
Authors: Febo Marcelo , González‐Rodríguez Loida A. , Capó‐Ramos David E. , González‐Segarra Naggai Y. , Segarra Annabell C.
Published: February 2004

Estrogen potentiates behavioral sensitization to cocaine in the female rat by mechanisms that remain undetermined. In this study, functional receptor autoradiography was used to investigate estrogen modulation of D2/D3 receptor‐induced G protein activation in components of the reward pathway of female rats treated acutely and repeatedly with cocaine. Rats were ovariectomized and given an empty (OVX group) or estradiol benzoate‐filled (OVX‐EB group) implant. After a week, animals received a daily saline or cocaine injection (15 mg/kg, i.p.) for 5 days, and again on day 13. Animals were killed, and brains were removed and cryosectioned. D2/D3‐stimulated [35S]guanosine 5′‐(γ‐thio) triphosphate (GTPγS) binding was assessed in the cingulate cortex area 2 (Cg2), striatum (STR), nucleus accumbens (NAc) and ventral tegmental area (VTA). OVX‐EB rats showed more [35S]GTPγS binding in the Cg2 and lower binding in the VTA than OVX rats; in the VTA this effect was reversed by a single cocaine injection. Repeated cocaine administration had opposite effects in OVX and OVX‐EB rats. [35S]GTPγS binding was decreased in the Cg2, NAc and STR of OVX‐EB rats, and increased in OVX rats. The present results support the hypothesis that cocaine‐induced changes in D2/D3 receptor activation are regulated by estrogen. These data suggest that changes in D2/D3 receptor function represent one mechanism by which estrogen regulates behavioral sensitization to cocaine.
Proteolipid plasmolipin: localization in polarized cells, regulated expression and lipid raft association in CNS and PNS myelin
Authors: Bosse Frank , Hasse Birgit , Pippirs Ulrich , Greiner‐Petter Regine , Müller Hans‐Werner
Published: February 2004

The proteolipid plasmolipin is member of the expanding group of tetraspan (4TM) myelin proteins. Initially, plasmolipin was isolated from kidney plasma membranes, but subsequent northern blot analysis revealed highest expression in the nervous system. To gain more insight into the functional roles of plasmolipin, we have generated a plasmolipin‐specific polyclonal antibody. Immunohistochemical staining confirms our previous observation of glial plasmolipin expression and proves plasmolipin localization in the compact myelin of rat peripheral nerve and myelinated tracts of the CNS. Western blot analysis indicates a strong temporal correlation of plasmolipin expression and (re‐) myelination in the PNS and CNS. However, following axotomy plasmolipin expression is also recovered in non‐regenerating distal nerve stumps. In addition, we detected plasmolipin expression in distinct neuronal subpopulations of the CNS. The observed asymmetric distribution of plasmolipin in compact myelin, as well as in epithelial cells of kidney and stomach, indicates a polarized cellular localization. Therefore, we purified myelin from the CNS and PNS and demonstrated an enrichement of phosphorylated plasmolipin protein in detergent‐insoluble lipid raft fractions, suggesting selective targeting of plasmolipin to the myelin membranes. The present data indicate that the proteolipid plasmolipin is a structural component of apical membranes of polarized cells and provides the basis for further functional analysis.
Swelling and deswelling kinetics of poly(N-isopropylacrylamide) gels
Authors: Takahashi Katsunori , Takigawa Toshikazu , Masuda Toshiro
Published: February 2004

Swelling and deswelling kinetics was investigated for three types of cylindrical poly(N-isopropylacrylamide) (PNIPA) gels differing in crosslink density. The temperature dependence curves of the volume of the gel specimens were different from one another. One of the gel specimens was considered as a critical gel showing the continuous volume phase transition. The volume change process of the specimens after a temperature jump was examined. In the deswelling processes with temperature jumps to temperatures higher than 35 °C, a phase separation was observed in the gel specimens and the volume change slowed down due to the homogenization after the phase separation. The value of the diffusion constant obtained without the phase separation decreased rapidly as temperature approaches the transition temperature. The rapid decrease for the critical gel indicates the emergence of the critical slowing-down. The value of the critical exponent for the correlation length suggests that the universality class for the volume phase transition of the critical PNIPA gel belongs to the class for the classical theory.
Dispersion corrections to density functionals for water aromatic interactions
Authors: Zimmerli Urs , Parrinello Michele , Koumoutsakos Petros
Published: February 2004

We investigate recently published methods for extending density functional theory to the description of long-range dispersive interactions. In all schemes an empirical correction consisting of a C6r−6 term is introduced that is damped at short range. The coefficient C6 is calculated either from average molecular or atomic polarizabilities. We calculate geometry-dependent interaction energy profiles for the water benzene cluster and compare the results with second-order Møller–Plesset calculations. Our results indicate that the use of the B3LYP functional in combination with an appropriate mixing rule and damping function is recommended for the interaction of water with aromatics.
Molecule intrinsic minimal basis sets. I. Exact resolution of ab initio optimized molecular orbitals in terms of deformed atomic minimal-basis orbitals
Authors: Lu W. C. , Wang C. Z. , Schmidt M. W. , Bytautas L. , Ho K. M. , Ruedenberg K.
Published: February 2004

A method is presented for expressing the occupied self-consistent-field (SCF) orbitals of a molecule exactly in terms of chemically deformed atomic minimal-basis-set orbitals that deviate as little as possible from free-atom SCF minimal-basis orbitals. The molecular orbitals referred to are the exact SCF orbitals, the free-atom orbitals referred to are the exact atomic SCF orbitals, and the formulation of the deformed “quasiatomic minimal-basis-sets” is independent of the calculational atomic orbital basis used. The resulting resolution of molecular orbitals in terms of quasiatomic minimal basis set orbitals is therefore intrinsic to the exact molecular wave functions. The deformations are analyzed in terms of interatomic contributions. The Mulliken population analysis is formulated in terms of the quasiatomic minimal-basis orbitals. In the virtual SCF orbital space the method leads to a quantitative ab initio formulation of the qualitative model of virtual valence orbitals, which are useful for calculating electron correlation and the interpretation of reactions. The method is applicable to Kohn–Sham density functional theory orbitals and is easily generalized to valence MCSCF orbitals.
Molecule intrinsic minimal basis sets. II. Bonding analyses for Si4H6 and Si2 to Si10
Authors: Lu W. C. , Wang C. Z. , Schmidt M. W. , Bytautas L. , Ho K. M. , Ruedenberg K.
Published: February 2004

The method, introduced in the preceding paper, for recasting molecular self-consistent field (SCF) or density functional theory (DFT) orbitals in terms of intrinsic minimal bases of quasiatomic orbitals, which differ only little from the optimal free-atom minimal-basis orbitals, is used to elucidate the bonding in several silicon clusters. The applications show that the quasiatomic orbitals deviate from the minimal-basis SCF orbitals of the free atoms by only very small deformations and that the latter arise mainly from bonded neighbor atoms. The Mulliken population analysis in terms of the quasiatomic minimal-basis orbitals leads to a quantum mechanical interpretation of small-ring strain in terms of antibonding encroachments of localized molecular-orbitals and identifies the origin of the bond-stretch isomerization in Si4H6. In the virtual SCF/DFT orbital space, the method places the qualitative notion of virtual valence orbitals on a firm basis and provides an unambiguous ab initio identification of the frontier orbitals.
Numerical prediction of absolute crystallization rates in hard-sphere colloids
Authors: Auer S. , Frenkel D.
Published: February 2004

Special computational techniques are required to compute absolute crystal nucleation rates of colloidal suspensions. Using crystal nucleation of hard-sphere colloids as an example, we describe in some detail the novel computational tools that are needed to perform such calculations. In particular, we focus on the definition of appropriate order parameters that distinguish liquid from crystal, and on techniques to compute the kinetic prefactor that enters in the expression for the nucleation rate. In addition, we discuss the relation between simulation results and theoretical predictions based on classical nucleation theory.
Spin-locking of half-integer quadrupolar nuclei in nuclear magnetic resonance of solids: Creation and evolution of coherences
Authors: Ashbrook Sharon E. , Wimperis Stephen
Published: February 2004

Spin-locking of half-integer quadrupolar nuclei, such as 23Na (I=3/2) and 27Al (I=5/2), is of renewed interest owing to the development of variants of the multiple-quantum and satellite-transition magic angle spinning (MAS) nuclear magnetic resonance experiments that either utilize spin-locking directly or offer the possibility that spin-locked states may arise. However, the large magnitude and, under MAS, the time dependence of the quadrupolar interaction often result in complex spin-locking phenomena that are not widely understood. Here we show that, following the application of a spin-locking pulse, a variety of coherence transfer processes occur on a time scale of ∼1/ωQ before the spin system settles down into a spin-locked state which may itself be time dependent if MAS is performed. We show theoretically for both spin I=3/2 and 5/2 nuclei that the spin-locked state created by this initial rapid dephasing typically consists of a variety of single- and multiple-quantum coherences and nonequilibrium population states and we discuss the subsequent evolution of these under MAS. In contrast to previous work, we consider spin-locking using a wide range of radio frequency field strengths, i.e., a range that covers both the “strong-field” (ω1≫ωQPAS) and “weak-field” (ω1≪ωQPAS) limits. Single- and multiple-quantum filtered spin-locking experiments on NaNO2, NaNO3, and Al(acac)3, under both static and MAS conditions, are used to illustrate and confirm the results of the theoretical discussion.
Free energy simulations: Use of reverse cumulative averaging to determine the equilibrated region and the time required for convergence
Authors: Yang Wei , Bitetti-Putzer Ryan , Karplus Martin
Published: February 2004

A method is proposed for improving the accuracy and efficiency of free energy simulations. The essential idea is that the convergence of the relevant measure (e.g., the free energy derivative in thermodynamic integration) is monitored in the reverse direction starting from the last frame of the trajectory, instead of the usual approach, which begins with the first frame and goes in the forward direction. This simple change in the use of the simulation data makes it straightforward to eliminate the contamination of the averages by contributions from the equilibrating region. A statistical criterion is introduced for distinguishing the equilibrated (production) region from the equilibrating region. The proposed method, called reverse cumulative averaging, is illustrated by its application to the well-studied case of the alchemical free energy simulation of ethane to methanol.
Ab initio melting curve of copper by the phase coexistence approach
Authors: Vočadlo L. , Alfè D. , Price G. D. , Gillan M. J.
Published: February 2004

Ab initio calculations of the melting properties of copper in the pressure range 0–100 GPa are reported. The ab initio total energies and ionic forces of systems representing solid and liquid copper are calculated using the projector augmented wave implementation of density functional theory with the generalized gradient approximation for exchange-correlation energy. An initial approximation to the melting curve is obtained using an empirical reference system based on the embedded-atom model, points on the curve being determined by simulations in which solid and liquid coexist. The approximate melting curve so obtained is corrected using calculated free energy differences between the reference and ab initio system. It is shown that for system-size errors to be rendered negligible in this scheme, careful tuning of the reference system to reproduce ab initio energies is essential. The final melting curve is in satisfactory agreement with extrapolated experimental data available up to 20 GPa, and supports the validity of previous calculations of the melting curve up to 100 GPa.
Multilevel conductivity and conductance switching in supramolecular structures of an organic molecule
Authors: Bandyopadhyay Anirban , Pal Amlan J.
Published: February 2004

We have demonstrated conductance switching between multilevel states in devices based on Rose Bengal molecules embedded in supramolecular matrices. Two mechanisms, namely electroreduction and conformational change of the molecules, resulting in conjugation modification have been proposed to be applicable in these devices. In a low voltage region, reverse-bias induced electroreduction of Rose Bengal facilitated conjugation restoration in the backbone of the molecule and, hence, switching to a high-conducting state. At high biases, the two perpendicular planes present in Rose Bengal, which have permanent dipole moments, allowed forward-bias induced conformation change to occur, and results in conductance switching. We have demonstrated how the devices can switch between two pair of conducting states for random-access memory and read-only memory applications for several hours.
Thickness dependent magnetization states of Fe islands on W(110): From single domain to vortex and diamond patterns
Authors: Bode M. , Wachowiak A. , Wiebe J. , Kubetzka A. , Morgenstern M. , Wiesendanger R.
Published: February 2004

We have studied the thickness dependent domain configuration of single-crystal nanoscale Fe islands on W(110) by spin-polarized scanning tunneling microscopy. The experimental results are compared with micromagnetic calculations. For very thin islands, the uniaxial surface anisotropy of Fe/W(110) leads to a single domain state. With increasing island thickness, the magnetostatic energy becomes increasingly important resulting in different flux closure configurations.
Carbon nanotube field emitter arrays having an electron beam focusing structure
Authors: Choi Jun Hee , Zoulkarneev Andrei R. , Jin Yong Wan , Park Young Jun , Chung Deuk Seok , Song Byung Kwon , Han In Taek , Lee Hang Woo , Park Sang Hyun , Kang Ho Suk , Kim Ha Jong , Kim Jung Woo , Jung Jae Eun , Kim Jong Min , Baek Hong Gu , Yu Se Gi
Published: February 2004

An electron beam focusing structure was incorporated into the gated field emitter arrays where the emitters were screen-printed carbon nanotubes. The focusing structure was comprised of 8-μm-thick bulky SiOx focus gate insulator and Cr focus gate, and exhibited negligible leakage between the gate and the focus gate. In current–voltage measurements, it is found that the anode current strongly depends on both the focus gate and the anode bias voltages. Electron beams were focused well at the anode with a slight overfocusing effect, which is due to the wide electron beam divergence from carbon nanotubes. A new focusing structure based on the simulation is proposed to overcome the overfocusing.
Broad-band polarization conversion from a finite periodic structure in the microwave regime
Authors: Hallam B. T. , Lawrence C. R. , Hooper I. R. , Sambles J. R.
Published: February 2004

A reflection grating demonstrating extraordinarily broad-band polarization conversion in a nondiffractive regime has been studied at microwave frequencies. This single-element structure has been fabricated by electrolessly plating a metallic layer onto a stereo-lithographically produced resin profile. Angle-dependent microwave reflectivity data collected from the grating indicates polarization conversion of greater than 80% over a spectral bandwidth equivalent to the entire visible regime (factor of 2 in frequency). This supports an earlier publication in which it was predicted that a broad-band polarization converter could be created from a suitably profiled diffraction grating.
Terahertz electro-optic wavelength conversion in GaAs quantum wells: Improved efficiency and room-temperature operation
Authors: Carter S. G. , Ciulin V. , Sherwin M. S. , Hanson M. , Huntington A. , Coldren L. A. , Gossard A. C.
Published: February 2004

A 4-μm-thick sample containing 50 GaAs/AlGaAs asymmetric coupled quantum wells was driven with a strong terahertz (THz) electric field of frequency ωTHz and probed with a near-infrared (NIR) laser of frequency ωNIR. The THz beam modulated the probe to generate sidebands at ωNIR+nωTHz, where n is an integer. Up to 0.2% of the NIR laser power was converted into the n=+1 sideband at 20 K, and sidebands were observed up to room temperature. The strong THz fields also induced changes in the NIR absorption of the sample.
Improving organic transistor performance with Schottky contacts
Authors: Schroeder Raoul , Majewski Leszek A. , Grell Martin
Published: February 2004

Organic field-effect transistors (OFETs) with non-Ohmic contacts, e.g., pentacene with gold electrodes, exhibit a linearly growing threshold voltage with increased film thickness due to tunnel injection [R. Schroeder et al., Appl. Phys. Lett. 83, 3201 (2003)]. In this letter, we demonstrate gold/pentacene OFETs with a low threshold voltage independent of pentacene thickness. By doping the pentacene in the contact area with FeCl3 (iron-III-chloride), the metal-insulator-type tunneling barrier was changed to a metal-semiconductor Schottky barrier. Since the injection through a Schottky barrier depends on the potential and not on the electric field, the threshold voltage is no longer a function of the semiconductor thickness. Through selective doping of the area under the electrode, the channel remains undoped, and large on/off ratios are retained.